1. A cell, a resistor, a key and ammeter are arranged as shown in the circuit diagrams of Figure12.1. The current recorded in the ammeter will be

(a) maximum in (i)
(b) maximum in (ii)
(c) maximum in (iii)
(d) the same in all the cases

Solution
(d) the same in all the cases

The current will be same in all the circuits as there are no changes in any of the circuits.

2. In the following circuits (Figure 12.2), heat produced in the resistor or combination of resistors connected to a 12 V battery will be

(a) same in all the cases
(b) minimum in case (i)
(c) maximum in case (ii) 
(d) maximum in case (iii) 

Solution
(c) maximum in case (ii) 

The two resistors are connected in series. The total resistance will be less than individual resistances in figure (iii) as they are connected parallel. Higher resistance produces more heat.

3. Electrical resistivity of a given metallic wire depends upon
(a) its length
(b) its thickness
(c) its shape
(d) nature of the material

Solution

(d) nature of the material 

4. A current of 1 A is drawn by a filament of an electric bulb. Number of electrons passing through a cross section of the filament in 16 seconds would be roughly

(a) 10²⁰
(b) 10¹⁶
(c) 10¹⁸
(d) 10²³

Solution
(a) 10²⁰

Therefore, n = 10²⁰ electrons 
The number of electrons flowing is 10²⁰ electrons  

5. Identify the circuit (Figure 12.3) in which the electrical components have been properly connected. 

(a) (i)
(b) (ii)
(c) (iii)
(d) (iv)

Solution
(b) (ii) 

6. What is the maximum resistance which can be made using five resistors each of 1/5 Ω?
(a) 1/5 Ω
(b) 10 Ω
(c) 5 Ω
(d) 1 Ω

Solution
(d) 1 Ω

Maximum resistance is obtained when resistors are connected in series.

7. What is the minimum resistance which can be made using five resistors each of 1/5 Ω?
(a) 1/5 Ω
(b) 1/25 Ω
(c) 1/10 Ω
(d) 25 Ω

Solution
(b) 1/25 Ω

Minimum resistance is obtained when resistors are connected parallel 
1/R = 5 + 5 +5+ 5 + 5 = 25 Ω

R = 1/25 Ω

8. The proper representation of series combination of cells (Figure 12.4) obtaining maximum potential is

(a) (i) 

(b) (ii) 
(c) (iii) 
(d) (iv) 

Solution
(a) (i)

The positive terminal of next cell is adjacent to negative terminal of previous cell.

9. Which of the following represents voltage ? 

(a) Work done/(Current × Time) 
(b) Work done × Charge
(c) (Work done × Time)/Current 
(d) Work done × Charge × Time 

Solution

(a) Work done/(Current × Time) 

10. A cylindrical conductor of length l and uniform area of crossnsection A has resistance R. Another conductor of length 2l and resistance R of the same material has area of cross section
(a) A/2
(b) 3A/2
(c) 2A
(d) 3A

Solution

(c) 2A

⇒ A = 2A

11. A student carries out an experiment and plots the V-I graph of three samples of nichrome wire with resistances R1 , R2 and R3 respectively (Figure.12.5). Which of the following is true?

(a) R₁ = R₂ = R₃
(b) R₁ > R₂ > R₃
(c) R₃ > R₂ > R₁
(d) R₂ > R₃ > R₁

Solution
(c) R₃ > R₂ > R₁

Current flow is inversely proportional to resistance. Highest resistance will show least amount of current.

12. If the current I through a resistor is increased by 100% (assume that temperature remains unchanged), the increase in power dissipated will be
(a) 100 %
(b) 200 %
(c) 300 %
(d) 400 %

Solution
(c) 300 %

Heat generated is directly proportional to square of current. Therefore, when current doubles, the dissipation of heat will multiply by 4.

13.  The resistivity does not change if
(a) the material is changed
(b) the temperature is changed
(c) the shape of the resistor is changed
(d) both material and temperature are changed

Solution
(c) the shape of the resistor is changed

14. In an electrical circuit three incandescent bulbs A, B and C of rating 40 W, 60 W and 100 W respectively are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness?
(a) Brightness of all the bulbs will be the same
(b) Brightness of bulb A will be the maximum
(c) Brightness of bulb B will be more than that of A
(d) Brightness of bulb C will be less than that of B

Solution
(c) Brightness of bulb B will be more than that of A

As the three bulbs are connected in parallel, so the resistance of the combination would be less than arithmetic sum of individual resistances of all the bulbs. Therefore, there will be no negative effect on current flow. As a result, the bulbs will glow according to their wattage.

15. In an electrical circuit two resistors of 2 Ω and 4 Ω respectively are connected in series to a 6 V battery. The heat dissipated by the 4 Ω resistor in 5 s will be
(a) 5 J
(b) 10 J
(c) 20 J
(d) 30 J

Solution
(c) 20 J

Equivalent resistance of the circuit is R = 4+2 = 6Ω

Therefore, heat dissipated by 4 ohm resistor is, H = I^Rt = 20J

16. An electric kettle consumes 1 kW of electric power when operated at 220 V. A fuse wire of what rating must be used for it?
(a) 1 A
(b) 2 A
(c) 4 A
(d) 5 A

Solution
(d) 5 A

P=V ×I

Or, 1000 W= 220 V×I

17. Two resistors of resistance 2 Ω and 4 Ω when connected to a battery will have
(a) same current flowing through them when connected in parallel
(b) same current flowing through them when connected in series
(c) same potential difference across them when connected in series
(d) different p

Solution
(b) same current flowing through them when connected in series

In series combination the resistors receive a common current as the current does not get divided into branches.

18. Unit of electric power may also be expressed as
(a) volt ampere
(b) kilowatt hour
(c) watt second
(d) joule second

Solution
(b) kilowatt hour

Volt-ampere(VA) is the unit for apparent power. Watt second(also watt-second, symbol W s or W.s) is a derived unit of energy and is equivalent to the joule. The joule-second is the unit used for Planck’s constant.

Short Answer Questions 

19. A child has drawn the electric circuit to study Ohm’s law as shown in Figure 12.6. His teacher told that the circuit diagram needs correction. Study the circuit diagram and redraw it after making all corrections.

Solution

20. Three 2 Ω resistors, A, B and C, are connected as shown in Figure 12.7. Each of them dissipates energy and can withstand a maximum power of 18W without melting. Find the maximum current that can flow through the three resistors?

Solution

Current P = I²R
⇒ 18W = I² × 2Ω
⇒ I² = 18W/2Ω = 9
⇒ I = 3A
This is the maximum current that can flow through the three resistors.

21. Should the resistance of an ammeter be low or high? Give reason.

Solution

The resistance of an ammeter should be close to zero. Ideally it should be zero ohm. If the resistance of the ammeter is non-zero then the true current will be affected substantially.

22. Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 2 Ω in series with a combination of two resistors (4 Ω each) in parallel and a voltmeter across the parallel combination. Will the potential difference across the 2 Ω resistor be the same as that across the parallel combination of 4Ω resistors? Give reason.

Solution

Total resistance for parallel combination of 4Ω resistors can be calculated as follows:

1/R = 1/4 + 1/4 = 1/2 
⇒ R = 2Ω

This shows that the resistance of parallel combination is equal to resistance of the series resistor. Therefore, the potential difference across 2Ω resistance will be same as potential difference across the other two resistors which are connected in parallel.

23. How does use of a fuse wire protect electrical appliances?

Solution
The resistance of the fuse wire is greater than that of the main wiring. The fuse wire melts and breaks the circuit when there is significant increase in the electric current.. This prevents the damage of electrical appliance.

24. What is electrical resistivity? In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads 5 A. The reading of the ammeter decreases to half when the length of the wire is doubled. Why?

Solution
Resistivity is the property of the conductor through which it resists the flow of electric current. Resistivity for any particular material is unique. Resistance is directly proportional to length of conductor and inversely proportional to current flow. As the length is doubled, the resistance also doubles but current flow reduces to half. This is the reason why the ammeter reading decreases.

25. What is the commercial unit of electrical energy? Represent it in terms of joules.

Solution
Commercial unit of electrical energy is killowatt-hour

1 kw/hr = 1 kW h
= 1000 W × 60 × 60s
= 3.6 × 10⁶ J

26. A current of 1 ampere flows in a series circuit containing an electric lamp and a conductor of 5 Ω when connected to a 10 V battery. Calculate the resistance of the electric lamp. Now if a resistance of 10 Ω is connected in parallel with this series combination, what change (if any) in current flowing through 5 Ω conductor and potential difference across the lamp will take place? Give reason.

Solution

Let R be the resistance of the electric lamp.
In series total resistance = 5 + R

Therefore, R = 5 ohm
Now, potential drop across lamp + conductor = 10 V
Therefore, V across the lamp = I × R = 1 × 5 = 5 Volt

27. Why is parallel arrangement used in domestic wiring?

Solution

In domestic wiring, parallel arrangement is used as it provides the same potential difference across each electrical appliance.

28. B₁ , B₂ and B₃ are three identical bulbs connected as shown in Figure 12.8. When all the three bulbs glow, a current of 3A is recorded by the ammeter A.

(i) What happens to the glow of the other two bulbs when the bulb B₁ gets fused?
(ii) What happens to the reading of A₁ , A₂ , A₃ and A when the bulb B₂ gets fused?
(iii) How much power is dissipated in the circuit when all the three bulbs glow together?

Solution

(i) In parallel circuit, the potential difference does not get divided. Therefore, if one bulb is fused, then the glowing of other bulbs will not be affected.

(ii) Ammeter A shows a reading of 3A. This means each of the A_l, A₂, and A₃ show 1 A reading.

Now, P= I²R
= (3A)²× 1.5 Ω
= 13.5 W

Long Answer Questions 

29. Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another circuit another set of three bulbs of the same wattage are connected in parallel to the same source.
(a) Will the bulb in the two circuits glow with the same brightness? Justify your answer.
(b) Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason. 

Solution

(a) In series connection, the resistance of the bulbs will be three times the resistance of single bulb. Therefore, the current in the series combination will be one-third of the current in each bulb in parallel combination. This in parallel combination the bulbs will glow more brightly.

(b) In series combination, the bulbs will stop glowing as the circuit is broken and therefore the current is zero. However, in parallel connection the bulbs will continue to glow with the same brightness.

30. State Ohm’s law? How can it be verified experimentally? Does it hold good under all conditions? Comment.

Solution

Ohm’s law states that at constant temperature, the potential difference (voltage) across an ideal conductor is proportional to the current through it.
V/I = R

Verification of Ohm’s law 

Steps to be followed in order to verify the Ohm’s law:

• Set up a circuit as shown in figure. The circuit consists of a nichrome wire XY of length, say 0.5 m, an ammeter, a voltmeter and four cells of 1.5 V each.
• First use only one cell as the source in the circuit and note the reading in the ammeter I, for the current and reading of the voltmeter V for the potential difference across the nichrome wire XY in the circuit. Tabulate them in the Table given
• Next connect two cells in the circuit and again note down the respective readings of the ammeter and voltmeter.
• Repeat the above steps using three cells and then four cells in the circuit separately.

31. What is electrical resistivity of a material? What is its unit? Describe an experiment to study the factors on which the resistance of conducting wire depends.

Solution

The inherent property of a conductor by virtue of which it resists the flow of electric current is known as resistivity. Resistivity of each material is unique.

The SI unit of resistivity is Ω m. 

Experiment to study the factors on which the resistance of conducting wire depends:

Set up:

• Take a nichrome wire, a torch bulb, a 10 W bulb and an ammeter (0 –5 A range), a plug key and some connecting wires.
• Connect four dry cells of 1.5 V each in series with the ammeter leaving a gap XY in the circuit, as shown in Fig. 12.4.
• Complete the circuit by connecting the nichrome wire in the gap XY. Plug the key. Note down the ammeter reading. •Now, change the length of the nichrome wire and take the ammeter reading.
• Next, change the thickness of nichrome wire and note down the ammeter reading.
• After few steps, use copper wire for the experiment. Attach copper wire and note down the ammeter reading.
• One by one change the length and thickness of the copper wire and observe the ammeter reading.
• Repeat the steps with different materials. 

Observation:

It is observed that the resistance depends on:

• Material of conductor.
• Length of conductor.
• Area of cross section.

32. How will you infer with the help of an experiment that the same current flows through every part of the circuit containing three resistances in series connected to a battery?

Solution

• Connect the three resistors R₁, R₂, R₃ in series to make the circuit.
• Use ammeter to see the current flowing through the three resistors.
• Remove R₁ and take the reading of potential difference of R₂ and R₃
  
• Remove R₂ and take the reading of potential difference of R₁ and R₃

Observation:
Ammeter reading is same in each case. This shows same current flows across each resistors connected in series.

33. How will you conclude that the same potential difference (voltage) exists across three resistors connected in a parallel arrangement to a battery?

Solution

• Take three resistors RI. ity. and R₃ and connect them in parallel to make a circuit as shown in figure.
• Use voltmeter to take reading of potential difference of three resistors in parallel combination.
• Now, remove the resistor R₁ and take the reacting of potential difference of remaining resistors combination.
• Then, remove the resistor R, and take the reading of potential difference of remaining resistor.

Observation:

It is observed that in each case the voltmeter reading is the same. This shows that in parallel arrangement, same potential difference exists across each resistor.

34. What is Joule’s heating effect? How can it be demonstrated experimentally? List its four applications in daily life.

Solution

According to Joules heating effect, the heat produced in a resistor is:

• Directly proportional to square of current.
• Directly proportional to resistance.
• Directly proportional to the time of current flowing through the resistor.

This can be mathematically expressed as,
H = I² Rt
H is heating effect,
I is electric current,
R is resistance and
t is time

Experiment to demonstrate Joules law of heating 

• Take an immersion rod and connect it to a socket which in turn is connected to a regulator.
• It is important as the regulator controls the amount of current flowing through a device.
• Keeping the pointer of regulator at minimum reading, measure the time taken by immersion rod to heat a certain amount of water.
• Next, increase the pointer of regulator to the next level.
• Measure the time taken by immersion rod to heat the same amount of water.
• Repeat above step for higher levels on regulator to measure the time.

Observation:

It is observed that with increased electric current, the time required to heat the same amount of water decreases. This verifies the Joule’s Law of Heating.

Application:

The electric appliances like electric toaster, oven, electric kettle and electric heater work on the basis of heating effect of electric current.

35. Find out the following in the electric circuit given in Figure 12.9

(a) Effective resistance of two 8 Ω resistors in the combination
(b) Current flowing through 4 Ω resistor
(c) Potential difference across 4 Ω resistance
(d) Power dissipated in 4 Ω resistor
(e) Difference in ammeter readings, if any

Solution
(a) Since, two 8 Ω resistors are in parallel, then their effective resistance R_ρ is given by

1/ R_ρ = 1/R₁ + 1/R₂ = 1/8 + 1/8 = 1/4
= R_ρ = 4 Ω
(b) Total resistance in the circuit
R = 4 Ω + R_ρ = 4 Ω + 4 Ω = 8 Ω
Current through the circuit,
I = V/R = 8/8 = 1A
Thus, current through 4 Ω resistor is 1 A as 4 Ω and R_ρ are in series and same current flows through them.
(c) Potential difference across 4 Ω resistor is potential drop by the 4 Ω resistor.
i.e. V = IR = 1 × 4 = 4V
(d) Power dissipated in 4 Ω resistor
P = I²R = I² × 4 = 4
(e) There is no difference in the reading of ammeters A₁ and A₂ as same current flows through all elements in a series current.

1. Choose the incorrect statement from the following regarding magnetic lines of field
(a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points
(b) Magnetic field lines are closed curves
(c) If magnetic field lines are parallel and equidistant, they represent zero field strength
(d) Relative strength of magnetic field is shown by the degree of closeness of the field lines

Solution

(c) If magnetic field lines are parallel and equidistant, they represent zero field strength

Parallel lines of magnetic field represent uniform magnetic field.

2. If the key in the arrangement (Figure 13.1) is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are
(a) concentric circles
(b) elliptical in shape
(c) straight lines parallel to each other
(d) concentric circles near the point O but of elliptical shapes as we go away from it

Solution

(a) concentric circles

1. Which of the following is a non-renewable source of energy?
(a) Wood
(b) Sun
(c) Fossil fuels
(d) Wind

Solution
(b) Sun

Sources of energy which are present in limited amount and can’t be recycled once used are known as non-renewable sources of energy. Fossil fuels are non-renewable source of energy.

2. Acid rain happens because
(a) sun leads to heating of upper layer of atmosphere
(b) burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere
(c) electrical charges are produced due to friction amongst clouds
(d) earth atmosphere contains acids

Solution
(b) burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere

When rain water mixes with the oxides of carbon, nitrogen and sulphur in the atmosphere, acid rain takes place.

3. Fuel used in thermal power plants is
(a) water
(b) uranium
(c) biomass
(d) fossil fuels

Solution
(d) fossil fuels 

Coal is the major fossil fuel used in thermal power plants. Along with coal natural gas and petroleum are also used.

4. In a hydro power plant
(a) Potential energy possessed by stored water is converted into electricity
(b) Kinetic energy possessed by stored water is converted into potential energy
(c) Electricity is extracted from water
(d) Water is converted into steam to produce electricity

Solution
(a) Potential energy possessed by stored water is converted into electricity . 

Water in the dams possesses potential energy. This potential energy converts into kinetic energy when the water is released. This kinetic energy turns the turbines. Turbines in turn produce electricity.

5. Which is the ultimate source of energy?
(a) Water
(b) Sun
(c) Uranium
(d) Fossil fuels 

Solution
(b) Sun

Plants use solar energy to produce food. Fossil fuels are produced from dead plants. Hence directly or indirectly, sunlight is the source of all energy.

6. Which one of the following forms of energy leads to least environmental pollution in the process of its harnessing and utilisation?
(a) Nuclear energy
(b) Thermal energy
(c) Solar energy
(d) Geothermal energy

Solution
(c) Solar energy

In nuclear energy, metals like uranium are used which release harmful rays. In thermal energy, coal is used as a fuel. Burning of coal releases sulphur and carbon dioxide which causes air pollution. In geothermal energy, the energy is absorbed by the pressure which can sometimes be extremely hot and dangerous.

7. Ocean thermal energy is due to
(a) energy stored by waves in the ocean
(b) temperature difference at different levels in the ocean
(c) pressure difference at different levels in the ocean
(d) tides arising out in the ocean

Solution
(b) temperature difference at different levels in the ocean

Energy from the surface of the ocean is used to boil volatile liquids. Vapors from these are used to turn the turbine.

8. The major problem in harnessing nuclear energy is how to
(a) split nuclei?
(b) sustain the reaction?
(c) dispose off spent fuel safely?
(d) convert nuclear energy into electrical energy?

Solution
(c) dispose off spent fuel safely?

Nuclear plants produce highly radioactive materials. Thus disposing the nuclear waste in the environment will pose a major threat to the living organisms. Therefore, safe disposal of nuclear waste is a major problem in harnessing nuclear energy.

9. Which part of the solar cooker is responsible for green house effect?
(a) Coating with black colour inside the box
(b) Mirror
(c) Glass sheet
(d) Outer cover of the solar cooker

Solution
(c) Glass sheet 

The trapping of heat by the atmosphere leads to the greenhouse effect. Same thing happens in a solar cooker. Solar energy gets trapped which is then reflected by the glass sheet, this helps in cooking the food.

10. The main constituent of biogas is 
(a) methane 
(b) carbon dioxide 
(c) hydrogen 
(d) hydrogen sulphide 

Solution
(a) methane 

Methane gas is the major product of biogas. Around 70% of the gas is methane and remaining is ammonia and carbon dioxide.

11. The power generated in a windmill
(a) is more in rainy season since damp air would mean more air mass hitting the blades
(b) depends on the height of the tower
(c) depends on wind velocity
(d) can be increased by planting tall trees close to the tower

Solution
(c) depends on wind velocity

High speed winds will turn the turbine at a higher speed. This in turn will increase the production of electricity.

12. Choose the correct statement
(a) Sun can be taken as an inexhaustible source of energy
(b) There is infinite storage of fossil fuel inside the earth
(c) Hydro and wind energy plants are non polluting sources of energy
(d) Waste from a nuclear power plant can be easily disposed off

Solution
(a) Sun can be taken as an inexhaustible source of energy

Fossil fuels are exhaustible energy sources. Hydro and wind energy plants can change the environment and affect the land use, homes, and natural habitats there by having a large environmental impact. The disposal of waste from a nuclear power plant is the major issue faced by nuclear plant.

13. In a hydroelectric power plant more electrical power can be generated if water falls from a greater height because
(a) its temperature increases
(b) larger amount of potential energy is converted into kinetic energy
(c) the electricity content of water increases with height
(d) more water molecules dissociate into ions

Solution
(b) larger amount of potential energy is converted into kinetic energy

14. Choose the incorrect statement regarding wind power
(a) It is expected to harness wind power to minimum in open space
(b) The potential energy content of wind blowing at high altitudes is the source of wind power
(c) Wind hitting at the blades of a windmill causes them to rotate The rotation thus achieved can be utilised further
(d) One possible method of utilising the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator

Solution
(b) The potential energy content of wind blowing at high altitudes is the source of wind power

Kinetic energy of the wind runs the wind power.

15. Choose the incorrect statement
(a) We are encouraged to plant more trees so as to ensure clean environment and also provide bio-mass fuel
(b) Gobar-gas is produced when crops, vegetable wastes etc., decompose in the absence of oxygen (c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash
(d) Bio-mass is a renewable source of energy

Solution
(c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash

Methane is the main product of a biogas. Biogas burns with less smoke and does not produce residual ash.

Short Answer Questions 

16. Why is there a need to harness non-conventional sources of energy? Give two main reasons.

Solution
Following are the reasons to harness non-conventional sources of energy:

• In the near future, the conventional sources will get exhausted.
• Non-conventional source of energy do not cause environmental pollution.

17. Write two different ways of harnessing energy from ocean.

Solution
Different ways of harnessing energy form the ocean are:

1. Tidal energy
2. Ocean thermal energy

18. What steps would you suggest to minimise environmental pollution caused by burning of fossil fuels?

Solution
Steps to minimise pollution caused by burning of fossil fuels are as follows.

• Use of non-conventional sources of energy.
• Afforestion should be adopted to control air pollution.
• Smokeless appliances should be used.

19. What is the role of a plane mirror and a glass sheet in a solar cooker?

Solution
Plane mirror increases the intensity of solar energy as it reflects the sunlight. Glass sheet prevents the escape of heat from the solar cooker.

20. Mention three advantages of a solar cell?

Solution
Advantages of a solar cell areas follows.

• They are the source of renewable energy.
• They do not cause pollution.
• They require minimum maintenance.

21. What is biomass? What can be done to obtain bio-energy using biomass?

Solution
Biomass is the fuel obtained from organic material. The methods to obtain bio-energy using biomass are as follows:

• Using firewood as a fuel.
• Preparing cow dung cakes and using them as a fuel.
• Preparation of gobar gas.

22. What are the limitations in obtaining energy from wind?

Solution

Limitations in obtaining energy from wind are as follows:

• No continuous and consistent production.
• Area required for installation of wind power mill is large.
• Minimum wind speed should be 15 km/hour.

Long Answer Questions 

24. How can solar energy be harnessed? Mention any two limitations in using solar energy. How are these limitations overcome?

Solution

Solar energy can be harnessed by the following methods:

1. Solar Cookers and solar water heaters:
   Black surfaces are good absorbers of heat as compared to a white or a reflecting surface. This is used in solar cookers and solar water heaters. Solar cookers are covered with a glass plate. Solar energy trapped within the solar cooker gets reflected by the glass plate and this helps in cooking the food.
2. Solar Cell
   A typical cell when exposed to sunlight develops a voltage of 0.5–1 V and produces about 0.7 W of electricity. Solar panels are a large number of solar cells that deliver enough electricity for practical use.

Limitations of solar energy:

• Cannot be harnessed beyond a certain latitude.
• Cannot be harnessed during the night.
• Can only be harnessed at places where there is plenty of sunlight.
• It is an expensive source of energy.

Cheaper technologies must be discovered. Batteries can be used to store electrical energy form photovoltaic cells.

25. Make a list of conventional and non-conventional sources of energy. Give a brief description of harnessing one nonconventional source of energy.

Solution
Coal, petroleum, fire wood and tidal energy are conventional sources of energy. Solar energy, nuclear energy, Biogas, Tidal energy, Ocean thermal energy, wave energy etc. are non-conventional energy sources.

The various methods to harness non-conventional energy sources are:

• Solar cookers, solar water heaters, solar cells and solar panels harness the solar energy.
• Nuclear reactors convert nuclear power to electric energy.
• The sun heats the water at the surface of the sea while the water in lower sections is relatively cold. This temperature difference is exploited to obtain energy in ocean-thermal-energy conversion plants.
• The kinetic energy possessed by huge waves near the seashore can be trapped to generate electricity.

26. Why is there a need for harnessing non-conventional sources of energy? How can energy be harnessed from the sea in different ways?

Solution

Following are the reason for the need to harness non-conventional sources of energy:

• In the near future, the conventional sources of energy will get exhausted in the near future.
• Non-conventional source of energy do not cause environmental pollution. 

Energy can be harnessed from the sea in following ways:

• Tidal energy: Tidal energy is harnessed by construction of a dam. A turbine fixed at the opening of the dam converts tidal energy to electricity.
• Wave energy: Near the sea shore, the kinetic energy possessed by huge waves can be harnessed to generate electricity. Strong winds blowing across the sea, generate the waves.
• Ocean Thermal Energy: The sun heats the water at the surface of the sea or ocean while the water in deeper layers is relatively cold. This temperature difference can be used to obtain energy in ocean-thermal-energy conversion plants.

27. What are the environmental consequences of using fossil fuels? Suggest the steps to minimise the pollution caused by various sources of energy including non-conventional sources of energy.

Solution
The various environmental consequences of using fossil fuels are:

• Increased levels of carbon dioxide in the atmosphere lead to global warming.
• Sulphur oxides causes acid rain.
• Accumulation of smog in big cities which in turn reduces visibility
• Air pollution which might cause health hazards to humans and animals.

The steps to minimize the pollution caused by various sources of energy including non-conventional sources of energy are as follows:

• Use of public transport
• Use of vehicles like electric bikes and bi-cycle
• Adopting the 3R’s policy-reduce, reuse and recycle
• Planting of trees

28. Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.

Solution
Energy from various sources is considered to have been derived from the sun. This statement can be justified by the following points: 

• Plants trap sunlight and produce food which ultimately forms the biomass. Biomass gets converted to fossil fuels. So, in general the energy derived from the fossil fuels is indirectly harnessed from sunlight.
• Biomass helps in obtaining wood and gobar gas.
• The kinetic energy of the sun circulates the water on the earth.
• The heating of water in the oceans causes waves and tides. Therefore, sun is indirectly responsible for harnessing tidal, wave and geothermal energy.

29. What is biomass? Explain the principle and working of a biogas plant using a labelled schematic diagram.

Solution

The fuel obtained from organic material is known as biomass. The anaerobic decomposition of cow-dung, various plant materials, vegetable waste and sewage gives bio-gas.

The biogas plant has a dome-shaped structure built with bricks. A slurry of cow-dung and water is made in the mixing tank which is then fed to the digester. The digester does not any supply of oxygen. Anaerobic micro-organisms decompose the complex compounds of the slurry. The decomposition process is completed in a few days and gases like methane, carbon dioxide, hydrogen and hydrogen sulphide are generated. This gas is stored in the gas tank above the digester from which it can be drawn through pipes for use.

Bio-gas contains up to 75% methane, hence it is an excellent fuel. It burns without smoke, leaves no residue like ash in wood, charcoal and coal burning. The heating capacity of bio-gas is also high.

The slurry left behind can be used as a manure as it is rich in nitrogen and phosphorous.

1. Which one of the following is an artificial ecosystem?
(a) Pond
(b) Crop field
(c) Lake
(d) Forest

Solution
(b) Crop field

Crop field is a man made ecosystem.

2. In a food chain, the third trophic level is always occupied by
(a) carnivores
(b) herbivores
(c) decomposers
(d) producers

Solution
(a) carnivores

First trophic level is producers, second tropic level is herbivores and the third trophic level is occupied by carnivores.

3. An ecosystem includes
(a) all living organisms
(b) non-living objects
(c) both living organisms and non-living objects
(d) sometimes living organisms and sometimes non-living objects

Solution
(c) both living organisms and non-living objects

An ecosystem includes living and nonliving organisms along with their interactions.

4. In the given food chain, suppose the amount of energy at fourth trophic level is 5 kJ, what will be the energy available at the producer level?
Grass → Grasshopper → Frog → Snake → Hawk
(a) 5 k J
(b) 50 k J
(c) 500 k J
(d) 5000 k J

Solution
(d) 5000 k J

The available energy at a particular trophic level is 10 times that of the energy available at the next tropic level. Hence, energy at third level trophic level is 50kJ that at the second level trophic is500 kJ and at first level trophic level (Producer) is5000 kJ.

5. Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as
(a) eutrophication
(b) pollution
(c) biomagnification
(d) accumulation

Solution
(c) biomagnification

• Eutrophication is richness of nutrient beyond optimum level. Eutrophication occurs due to run off from land.
• Introduction of an undesired substance into environment. Pollution leads to harmful effects on living organisms.

17. In the given Figure 15.1 the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?

(a) T₄
(b) T₂
(c) T₁
(d) T₃

1. From the list given below pick the item that is not a natural resource
(a) Soil
(b) Water
(c) Electricity
(d) Air

Solution
(c) Electricity

Soil, water and air are natural resources whereas electricity is produced by humans.

2. The most rapidly dwindling natural resource in the world is
(a) water
(b) forests
(c) wind
(d) sunlight

Solution
(b) forests

Water, wind and sunlight are non-exhaustible resources. But due to human activities, forests are depleting.

3. The most appropriate definition of a natural resource is that it is a substance/commodity that is
(a) present only on land
(b) a gift of nature which is very useful to mankind
(c) a man-made substance placed in nature
(d) available only in the forest

Solution
(b) a gift of nature which is very useful to mankind

Natural resources are not man made and they are present everywhere on earth.

4. The main cause for abundant coliform bacteria in the river Ganga is
(a) disposal of unburnt corpses into water
(b) discharge of effluents from electroplating industries
(c) washing of clothes
(d) immersion of ashes

Solution
(a) disposal of unburnt corpses into water

Human excreta mainly contain coliforms. Therefore, unburnt corpses are the sources of coliform which pollute Ganga river water.

5. The pH of water sample collected from a river was found to be acidic in the range of 3.5 – 4.5, on the banks of the river were several factories that were discharging effluents into the river. The effluents of which one of the following factories is the most likely cause for lowering the pH of river water? 

(a) Soap and detergent factory
(b) Lead battery manufacturing factory
(c) Plastic cup manufacturing factory
(d) Alcohol distillery

Solution
(d) Alcohol distillery

Acid spillage from lead battery manufacturing factory can lower down the pH.

6. The pH range most conducive for life of fresh water plants and animals is
(a) 6.5 – 7.5
(b) 2.0 – 3.5
(c) 3.5 – 5.0
(d) 9.0 – 10.5

Solution
(a) 6.5 – 7.5

Neutral pH is the most conducive for life of fresh water plants and animals.

7. The three R’s that will help us to conserve natural resources for long term use are
(a) recycle, regenerate, reuse
(b) reduce, regenerate, reuse
(c) reduce, reuse, redistribute
(d) reduce, recycle, reuse

Solution
(d) reduce, recycle, reuse

Reduce, recycle and reuse can conserve the natural resources.

8. Given below are a few statements related to biodiversity. Pick those that correctly describe the concept of biodiversity 

(i) Biodiversity refers to the different species of flora and fauna present in an area
(ii) Biodiversity refers to only the flora of a given area
(iii) Biodiversity is greater in a forest
(iv) Biodiversity refers to the total number of individuals of a particular species living in an area 

(a) (i) and (ii)
(b) (ii) and (iv)
(c) (i) and (iii)
(d) (ii) and (iii)

Solution
(c) (i) and (iii)

Biodiversity includes flora and fauna and it does not describe just one species.

9. Among the statements given below select the ones that correctly describe the concept of sustainable development
(i) Planned growth with minimum damage to the environment
(ii) Growth irrespective of the extent of damage caused to the environment
(iii) Stopping all developmental work to conserve the environment
(iv) Growth that is acceptable to all the stakeholders 

(a) (i) and (iv)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (iii) only

Solution
(a) (i) and (iv)

Sustainable development refers to planned growth with minimum damage to the environment while keeping the future of coming generation in mind.

10. In our country, vast tracts of forests are cleared and a single species of plant is cultivated. This practice promotes
(a) biodiversity in the area
(b) monoculture in the area
(c) growth of natural forest
(d) preserves the natural ecosystem in the area

Solution
(b) monoculture in the area

Monoculture is cultivation of a single species of plant.

11. A successful forest conservation strategy should involve
(a) protection of animals at the highest trophic level
(b) protection of only consumers
(c) protection of only herbivores
(d) comprehensive programme to protect all the physical and biological components

Solution
(d) comprehensive programme to protect all the physical and biological components

Balance in the biotic and abiotic community is very essential in the conservation of forests.

12. The important message conveyed by the ‘Chipko Movement’ is
(a) to involve the community in forest conservation efforts
(b) to ignore the community in forest conservation efforts
(c) to cut down forest trees for developmental activities
(d) government agencies have the unquestionable right to order destruction of trees in forests

Solution
(a) to involve the community in forest conservation efforts

'Chipko Movement' represents sacred feelings of community towards the local forest areas.

13. In our country, there are attempts to increase the height of several existing dams like Tehri and Almati, dams across Narmada. Choose the correct statements among the following that are a consequence of raising the height of dams
(i) Terrestrial flora and fauna of the area is destroyed completely
(ii) Dislocation of people and domestic animals living in the area
(iii) Valuable agricultural land may be permanently lost
(iv) It will generate permanent employment for people 

(a) (i) and (ii)
(b) (i), (ii) and (iii)
(c) (ii) and (iv)
(d) (i), (iii) and (iv)

Solution
(d) (i), (iii) and (iv)

Dam construction causes destruction of downstream agricultural land and adversely affects the living organisms present there.

14. Expand the abbreviation GAP
(a) Governmental Agency for Pollution Control
(b) Gross Assimilation by Photosynthesis
(c) Ganga Action Plan
(d) Governmental Agency for Animal Protection

Solution
(c) Ganga Action Plan

15. Select the incorrect statement
(a) Economic development is linked to environmental conservation
(b) Sustainable development encourages development for current generation and conservation of resources for future generations
(c) Sustainable development does not consider the view points of stakeholders
(d) Sustainable development is a long planned and persistent development

Solution
(c) Sustainable development does not consider the view points of stakeholders

Sustainable developments take into consideration both economic growth and ecological conservation simultaneously.

16. Which of the following is not a natural resource?
(a) Mango tree
(b) Snake
(c) Wind
(d) Wooden house

Solution
(d) Wooden house

Resources that occur naturally within environment are called as natural resources.

17. Select the wrong statement
(a) Forests provide variety of products
(b) Forests have greater plant diversity
(c) Forests do not conserve soil
(d) Forests conserve water

Solution
(c) Forests do not conserve soil

Forests prevent soil erosion, add fertility to the soil by adding humus, and thus they conserve the soil and its fertility.

18. Arabari forests of Bengal is dominated by
(a) Teak
(b) Sal
(c) Bamboo
(d) Mangroove

Solution
(b) Sal

Arabari forests of Bengal are dominated by sal trees.

19. Ground water will not be depleted due to
(a) afforestation
(b) thermal power plants
(c) loss of forest, and decreased rainfall
(d) cropping of high water demanding crops

Solution
(b) thermal power plants

The roots of the plants make the soil pervious. Thus, afforestation helps in recharging the ground water.

20. Opposition to the construction of large dams is due to
(a) social reasons
(b) economic reasons
(c) environmental reasons
(d) all the above

Solution
(d) all the above

The ecosystem near the dam is destroyed. This is an environmental reason. Relocation of people is a social reason. Agricultural land and employment are economic reasons.

21. Khadins, Bundhis, Ahars and Kattas are ancient structures that are examples for
(a) grain storage
(b) wood storage
(c) water harvesting
(d) soil conservation

Solution
(c) water harvesting

22. Pick the right combination of terms which has no fossil fuel.
(a) Wind, ocean and coal
(b) Kerosene, wind and tide
(c) Wind, wood, sun
(d) Petroleum, wood, sun

Solution
(c) Wind, wood, sun

Coal, kerosene and petroleum are fossil fuels.

23. Select the eco-friendly activity among the following
(a) Using car for transportation
(b) Using polybags for shopping
(c) Using dyes for colouring clothes
(d) Using windmills to generate power for irrigation

Solution
(d) Using windmills to generate power for irrigation

Using car for transportation, using polybags and dyes for coloring clothes increases the environmental pollution.

24. It is important to make small check dams across the flooded gullies because they
(i) hold water for irrigation
(ii) hold water and prevent soil erosion
(iii) recharge ground water
(iv) hold water permanently 

(a) (i) and (iv)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (ii) and (iv)

Solution
(b) (ii) and (iii)

Check dams prevent soil erosion. Check dams also help in improvement of groundwater level by holding the water.

Short Answer Questions 

25. Prepare a list of five items that you use daily in the school. Identify from the list such items that can be recycled.

Solution
The following items are used in our daily life in schools: paper, rexin bag, blade, pen, plastic box, scale, eraser, compass and dividers (metallic), steel lunch box, steel spoon.

Paper, blade, plastic box, eraser, compass, steel lunch box and steel spoon can be recycled.

26. List two advantages associated with water harvesting at the community level.

Solution
Two advantages associated with water harvesting at the community level are:

• Due to recharging of wells the ground water level increases.
• Ground water keeps the layers of soil above it moist and prevents loss of water by evaporation.

27. In a village in Karnataka, people started cultivating crops all around a lake which was always filled with water. They added fertilisers to their field in order to enhance the yield. Soon they discovered that the waterbody was completely covered with green floating plants and fishes started dying in large numbers.
Analyse the situation and give reasons for excessive growth of plants and death of fish in the lake.

Solution
Excessive use of fertilisers in the fields carried the chemicals down to the lake during rains. Many fertilisers contain phosphates and nitrates. The surface of water gets completely covered with plants as these chemicals promote excessive growth of aquatic plants. This process is known as eutrophication. This in turn depletes the availability of light, dissolved oxygen and nutrients in water, thereby resulting in the death of fishes.

28. What measures would you take to conserve electricity in your house?

Solution

The measures taken to conserve electricity in our houses are as follows:

• Put off the fans and lights when they are not in use.
• Maximum use of solar radiation.
• During winters, use solar water heating system.
• Use of fluorescent tubes or CFL.

29. Although coal and petroleum are produced by degradatioin of bio- mass, yet we need to conserve them. Why?

Solution
Both the energy sources take millions of years for their formation. These resources are being utilised at a much faster rate than their formation rate, hence they will be exhausted in the near future. This is the reason why they need to be conserved.

30. Suggest a few measures for controlling carbon dioxide levels in the atmosphere.

Solution

31. (a) Locate and name the water reservoirs in Figures16.1 (a) and (b).
(b) Which has an advantage over the other and why?

(a) The water reservoir is a pond in Figure 16.1 (a) and underground water body in the Figure 16.1 (b).

(b) Figure 16.1 (b) has more advantage than Figure 16.1 (a), because of the following reasons:

• Water does not evaporate.
• Water is spread out to recharge wells.
• Water provides moisture for vegetation over a wide area.
• Water is protected from contamination by animal and human wastes.
• Water prevents breeding of insects

1. Which one of the following sets of phenomena would increase on raising the temperature?
(a) Diffusion, evaporation, compression of gases
(b) Evaporation, compression of gases, solubility
(c) Evaporation, diffusion, expansion of gas
(d) Evaporation, solubility, diffusion, compression of gases

Solution

(c) Evaporation, diffusion, expansion of gas
The particles of matter possess kinetic energy as they are continuously moving. Increase in kinetic energy increases the rate of diffusion. Evaporation is the conversion of liquid state into vapour state. As the temperature is increased the molecules move and vibrate quickly, this enables them to escape into the atmosphere in the form of vapours. Increase in temperature also causes the molecules move faster, this results in expansion of gases.

2. Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of conditions :
(a) Low temperature, low pressure
(b) High temperature, low pressure
(c) Low temperature, high pressure
(d) High temperature, high pressure

Solution

(c) Low temperature, high pressure

3. The property to flow is unique to fluids. Which one of the following statements is correct?
(a) Only gases behave like fluids
(b) Gases and solids behave like fluids
(c) Gases and liquids behave like fluids
(d) Only liquids are fluids

Solution

(c) Gases and liquids behave like fluids

The intermolecular force of attraction between the particles is less in case of gases and liquids. This facilitates the flow of gases and liquids.

4. During summer, water kept in an earthen pot becomes cool because of the phenomenon of :
(a) diffusion
(b) transpiration
(c) osmosis
(d) evaporation

Solution

5. A few substances are arranged in the increasing order of ‘forces of attraction’ between their particles. Which one of the following represents a correct arrangement ?
(a) Water, air, wind
(b) Air, sugar, oil
(c) Oxygen, water, sugar
(d) Salt, juice, air

Solution

(c) Oxygen, water, sugar
Intermolecular forces of attraction are least in gases than liquids and most in solids. Oxygen is a gas, water is a liquid and sugar is a crystalline solid.

6. On converting 25°C, 38°C and 66°C to Kelvin scale, the correct sequence of temperature will be :
(a) 298 K, 311 K and 339 K
(b) 298 K, 300 K and 338 K
(c) 273 K, 278 K and 543 K
(d) 298 K, 310 K and 338 K

Solution

(a) 298 K, 311 K and 339 K
Add 273 to respective temperature to get temperature in kelvin.
25° + 273 = 298K
38° + 273 = 311K
66° + 273 = 339K

7. Choose the correct statement of the following :
(a) Conversion of solid into vapours without passing through the liquid state is called vaporization.
(b) Conversion of vapours into solid without passing through the liquid state is called sublimation.
(c) Conversion of vapours into solid without passing through the liquid state is called freezing.
(d) Conversion of solid into liquid is called sublimation.

Solution

(b) Conversion of vapours into solid without passing through the liquid state is called sublimation.
Sublimation is the process in which a solid changes into vapours without passing through the liquid state. Vaporisation is a phase transition from liquid to vapour phase. Conversion of liquid to solid at the freezing temperature is called freezing.

8. The boiling points of diethyl ether, acetone and n-butyl alcohol are 35°C, 56°C and 118°C respectively. Which one of the following correctly represents their boiling points in Kelvin scale?
(a) 306 K, 329 K, 391 K
(b) 308 K, 329 K, 392 K
(c) 308 K, 329 K, 391 K
(d) 329 K, 392 K, 308 K

Solution

(c) 308 K, 329 K, 391 K
Temperature expressed in Celsius can be converted into kelvin by adding 273. Boiling points of diethyl ether, acetone and n-butyl alcohol are 308 K, 329 K, and 391 K respectively.

9. Which condition out of the following will increase the evaporation of water?
(a) Increase in temperature of water
(b) Decrease in temperature of water
(c) Less exposed surface area of water
(d) Adding common salt to water

Solution

(a) Increase in temperature of water
Increasing the temperature of water increases the kinetic energy of the water. Because of this more particles attain energy which is sufficient to convert into vapour state. This is the reason why an increase in temperature increases the rate of evaporation.

10. In which of the following conditions, the distance between the molecules of hydrogen gas would increase?
(i) Increasing pressure on hydrogen contained in a closed container.
(ii) Some hydrogen gas leaking out of the container.
(iii) Increasing the volume of the container of hydrogen gas.
(iv) Adding more hydrogen gas to the container without increasing the volume of the container.
(a) (i) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and ( (iv)

Solution

(c) (ii) and (iii)
Either the volume of hydrogen gas should be reduced or the volume of the container should be increased in order to increase the intermolecular interaction. The inter-molecular interaction would also decrease if the pressure is increased or hydrogen is added without increasing container volume.

Short Answer Questions

11. A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure? Will this water freeze at 0°C? Comment.

Solution

The boiling point and melting point of pure water at 1 atmospheric pressure are100 °C is 0°C respectively. In the question, it is given that the water boils at 102°C, this means that the water is not pure.
The water will freeze at temperature below 0°C.

12. A student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time. Which of the following figure would correctly represent the result? Justify your choice.

Solution

Graph (d) correctly represents the result. This is because the temperature of the mixture will be 0° at the start of the experiment as water and ice are in equilibrium. Now, as the students start heating, initially heat will be utilised to melt the ice. Therefore, there will be no change in temperature for certain amount of time. When the students heat the mixture further the temperature of the water increases.

13. Fill in the blanks :
(a) Evaporation of a liquid at room temperature leads to a _____ effect.
(b) At room temperature the forces of attraction between the particles of solid substances are_____ than those which exist in the gaseous state.
(c) The arrangement of particles is less ordered in the_____ state. However, there is no order in the _____ state.
(d) _____ is the change of gaseous state directly to solid state without going through the _____ state.
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called _____.

Solution

(a) Evaporation of a liquid at room temperature leads to a cooling effect.

(b) At room temperature the forces of attraction between the particles of solid substances are stronger than those which exist in the gaseous state.

(c) The arrangement of particles is less ordered in the liquid state. However, there is no order in the gaseous state.

(d) Sublimation is the change of solid state directly to vapour state without going through the liquid state.

(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called evaporation.

14. Match the physical quantities given in column A to their SI units given in column B :

A	B
(a) Pressure	(i) cubic metre
(b) Temperature	(ii) kilogram
(c) Density	(iii) pascal
(d) Mass	(iv) kelvin
(e) Volume	(v) kilogram per cubic metre

Solution

A	B
(a) Pressure	(iii) pascal
(b) Temperature	(iv) kelvin
(c) Density	(v) kilogram per cubic metre
(d) Mass	(ii) kilogram
(e) Volume	(i) cubic metre

15. The non-SI and SI units of some physical quantities are given in column A and column B respectively. Match the units belonging to the same physical quantity :

A	B
(a) degree Celsius	(i) kilogram
(b) centimeter	(ii) pascal
(c) gram per centimeter cube	(iii) metre
(d) bar	(iv) kelvin
(e) miligram	(v) kilogram per metre cube

Solution

A	B
(a) degree Celsius	(iv) kelvin
(b) centimeter	(iii) metre
(c) gram per centimeter cube	(v) kilogram per metre cube
(d) bar	(ii) pascal
(e) miligram	(i) kilogram

16. ‘Osmosis is a special kind of diffusion.’ Comment.

Solution

Yes, osmosis is a special kind of diffusion. This is because there is movement of particles from regions of higher concentration to regions of lower concentration. But in osmosis the movement of solvent is through a semi permeable membrane which is permeable only to water molecules.

17. Classify the following into osmosis/diffusion :
(i) Swelling up of a raisin on keeping in water.
(ii) Spreading of virus on sneezing.
(iii) Earthworm dying on coming in contact with common salt.
(iv) Shrinking of grapes kept in thick sugar syrup.
(v) Preserving pickles in salt.
(vi) Spreading of smell of cake being baked throughout the house.
(vii) Aquatic animals using oxygen dissolved in water during respiration.

Solution

(i) Osmosis
(ii) Diffusion
(iii) Osmosis
(iv) Osmosis
(v) Osmosis
(vi) Diffusion
(vii) Diffusion

18. Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.

Solution

The water molecules have low energy incase of ice whereas in the case of steam the water molecules have high energy. This high energy of water molecules in case of steam is transformed and may cause burns. On the other hand, the water molecules in case of ice take heat energy from the body thereby producing a cooling effect.

19. Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Comment.

Solution

The temperature of both boiling water and steam is 100°C, but steam has more energy because of latent heat of vapourisation.

20. A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs (fig.) would correctly represent the change in its temperature as a function of time.

Solution

Graph (a) correctly represents the change in the temperature of the content of the glass tumbler as a function of time. This can be explained as the water cools initially, it reaches 0°C, i.e. the freezing point. At this stage the temperature will remain constant till all the water freezes. The temperature falls again after this temperature.

21. Look at fig. and suggest in which of the vessels A, B, C or D the rate of evaporation will be the highest. Explain.

Solution

The rate of evaporation will be maximum in case of vessel c.

This is because evaporation is a surface phenomenon. Hence the rate of evaporation increases with an increase of surface area. Also, the particles of water vapour will move away with the air when there is an increase in air speed, this also increases the rate of evaporation.

22. (a) Conversion of solid to vapour is called sublimation. Name the term used to denote the conversion of vapour to solid.
(b) Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion?

Solution

(a) Conversion of vapour to solid is known as deposition.

(b) Latent heat of fusion is the amount of heat required to melt1 kg of solid into liquid at one atmosphere pressure at its melting point.\

Long Answer Questions

23. You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with well labelled diagram.

Solution

Naphthalene being a non-polar compound is insoluble in water but soluble in ether an organic solvent. Also, it is volatile at room temperature. Similarly, ammonium chloride is a polar compound and thus soluble in water. It is also volatile at higher temperature. By decantation of aqueous mixture, the mixture of naphthalene and ammonium chloride can be separated. Naphthalene remains undissolved in water and can be separated out in the funnel. The filtrate of ammonium chloride can be evaporated to obtain dry ammonium chloride.

24. It is a hot summer day, Priyanshi and Ali are wearing cotton and nylon clothes respectively. Who do you think and would be more comfortable and why?

Solution

Cotton absorbs the sweat as it is a better absorber of water than nylon. Further evaporation of sweat form the cotton shirt will lead to cooling. Hence Priyanshi is more comfortable.

25. Cotton being a better absorber of water than nylon and helps in absorption of sweat followed by evaporation which leads to cooling. So, Priyanshi is more comfortable, whereas Ali is not so comfortable.

Solution

The following conditions can increase the rate of evaporation of water:

• Increase the surface area by spreading the shirt.
• Increase the temperature by putting the shirt under the sun.
• Increase the wind speed by spreading it under the fan.

26. Comment on the following statements :
(a) Evaporation produces cooling.
(b) Rate of evaporation of an aqueous solution decreases with increase in humidity.
(c) Sponge though compressible is a solid.

Solution

(a) The particles at the surface of the liquid gain energy from the surroundings and change into vapour. This is the reason why evaporation produces a cooling effect.

(b) Humidity is the amount of water vapour content in the air around us. Air has a definite capacity to hold water vapour at a given temperature. So, if the air already has water vapour, it cannot take up more water. This is the reason why the rate of evaporation decreases in humidity.

(c) Sponge has minute holes with trapped air. The material of the sponge is not rigid. The air present in the holes gets expelled when a sponge is pressed, this is the reason why it can be compressed.

27. Why does the temperature of a substance remain constant during its melting point or boiling point?

Solution

At the melting and boiling point, the temperature of a substance remains constant until all the substance melts or boils. This happens because the heat supplied is used in overcoming the forces of attraction between the particles and thereby changing the state of the substance. Latent heat of fusion or the latent heat of vaporisation is this heat energy absorbed without showing any rise in temperature.

1. Which of the following statements are true for pure substances?
(i) Pure substances contains only one kind of particles.
(ii) Pure substances may be compounds or mixtures.
(iii) Pure substances have the same composition throughout.
(iv) Pure substances can be exemplified by all elements other than nickel.
(a) (i) and (ii)
(b) (i) and (iii)
(c) (iii) and (iv)
(d) (ii) and (iii)

Solution

(b) (i) and (iii)

2. Rusting of an article made up of iron is called :
(a) corrosion and it is a physical as well as chemical change.
(b) dissolution and it is a physical change.
(c) corrosion and it is a chemical change.
(d) dissolution and it is a chemical change.

Solution

(c) corrosion and it is a chemical change.
Rusting of iron is also known as corrosion and it is a chemical change because rust is a chemical compound called hydrated iron oxide Fe₂O₃. nH₂O, iron(III) which is different from elemental iron.

3. A mixture of sulphur and carbon disulphide is :
(a) heterogeneous and shows Tyndall effect.
(b) homogeneous and shows Tyndall effect.
(c) heterogeneous and does not show Tyndall effect.
(d) homogeneous and does not show Tyndall effect.

Solution

(d) homogeneous and does not show Tyndall effect.
A mixture of sulphur and carbon disulphide is heterogeneous in nature and it shows Tyndall effect. This happens because the particles are big enough to scatter light.

4. Tincture of iodine has antiseptic properties. This solution is made by dissolving :
(a) Iodine in potassium iodide
(b) Iodine in vaseline
(c) Iodine in water
(d) Iodine in alcohol

Solution

(d) Iodine in alcohol.
Tincture is prepared by using2-7% elemental iodine, either potassium iodide or sodium dissolved in alcohol. Alcohol is a good solvent and iodine does not dissolve in water, so alcohol should be used.

5. Which of the following are homogeneous in nature?
(i) Ice
(ii) Wood
(iii) Soil
(iv) Air
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (iv)
(d) (iii) and (iv)

Solution

(c) (i) and (iv)
Air and ice are homogeneous mixture as their constituents are not visible and cannot be distinguished from one another.

6. Which of the following are physical changes?
(i) Melting of iron metal
(ii) Rusting of iron
(iii) Bending of an iron rod
(iv) Drawing a wire of iron metal
(a) (i), (ii) and (iii)
(b) (i), (ii) and (iv)
(c) (i), (iii) and (iv)
(d) (ii), (iii) and (iv)

Solution

(c) (i), (iii) and (iv)
During the process of rusting of iron, iron reacts with water and oxygen to produce iron oxide, hence it is a chemical change.

7. Which of the following are chemical changes?
(i) Decaying of wood
(ii) Burning of wood
(iii) Sawing of wood
(iv) Hammering of a nail into a piece of wood
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)

Solution

(a) (i) and (ii)
Decaying of wood and burning of wood are chemical changes as there will be a change of chemical composition and wood cannot be restored to its original form.

8. Two substances, A and B were made to react to form a third substance, A₂B according to the following reaction
2A + B → A₂B
Which of the following statements concerning this reaction are incorrect?
(i) The product A₂B shows the properties of substances A and B.
(ii) The product will always have a fixed composition.
(iii) The product so formed cannot be classified as a compound.
(iv) The product so formed is an element.
(a) (i), (ii) and (iii),
(b) (ii), (iii) and (iv)
(c) (i), (iii) and (iv)
(d) (ii), (iii) and (iv)

Solution

(c) (i), (iii) and (iv)

A₂B is a compound made up of two elements A and B in a fixed ratio. The properties of a compound (e.g., A₂B) are entirely different from those of its constituent elements (i.e. A and B). The composition of a compound is fixed.

9. Two chemical species X and Y combine together to form a product P which contains both X and Y
X + Y → P
X and Y cannot be broken down into simpler substances by simple chemical reactions. Which of the following concerning the species X, Y and P are correct?
(i) P is a compound.
(ii) X and Y are compounds.
(iii) X and Y are elements.
(iv) P has a fixed composition.
(a) (i), (ii) and (iii)
(b) (i), (ii) and (iv)
(c) (ii), (iii) and (iv)
(d) (i), (iii) and (iv)

Solution

(d) (i), (iii) and (iv)
As X and Y cannot be further broken down into simpler substances, they are elements. P can be broken down to simpler substances hence it is a compound with a fixed composition.

Short Answer Questions

10. Suggest separation technique(s) one would need to employ to separate the following mixtures :

(i) Mercury and water
(ii) Potassium chloride and ammonium chloride
(iii) Common salt, water and sand
(iv) Kerosene oil, water and salt

Solution

(i) Separation by using separating funnel (used for separating two immiscible liquids). The principle is that immiscible liquids separate out in layers depending on their densities.
(ii) Sublimation : It is a process by which solid changes directly into gas and vice versa without passing
through the liquid state. Ammonium chloride is sublime.
(iii) Filtration followed by evaporation or centrifugation followed by evaporation/distillation.
(iv) Separation by using separating funnel to separate kerosene oil followed by evaporation or distillation.

11. Salt can be recovered from its solution by evaporation. Suggest some other technique for the same.

Solution

Salt can be recovered from its solution by crystallization. Crystallization removes soluble impurities which are not removed in case of evaporation. Hence it is a more efficient process.

12. Which of the tubes in figure given here (a) and (b) will be more effective as a condenser in the distillation apparatus?

Solution

Beads in tube A increase the surface area for the cooling of vapours that come in contact with them. Hence, tube A is a good condenser.

13. The ‘sea water’ can be classified as a homogeneous as well as heterogeneous mixture. Comment.

Solution

The sea water on the surface is a homogenous mixture as it comprises of water and salts. Whereas the sea water from deep sea consists of salts, water, mud, decayed plants etc. hence it will be a heterogeneous mixture.

14. While diluting a solution of salt in water, a student by mistake added acetone (boiling point 56°C). What technique can be employed to get back the acetone? Justify your choice.

Solution

Fractional distillation can be used to separate acetone from the mixture of salt and water. There is a considerable difference in the boiling points of acetone (56°C) and water (100°C). Acetone evaporates first when the solution is heated. The water is collected in the distillation flask. The vapours of acetone are then condensed to obtain acetone.

15. What would you observe when :
(i) A saturated solution of potassium chloride prepared at 60°C is allowed to cool at room temperature?
(ii) An aqueous sugar solution is heated to dryness?
(iii) A mixture of iron filings and sulphur powder is heated strongly?

Solution 

(a) Solid potassium chloride will separate out.

(b) The water will evaporate initially and then sugar will get charred.

(c) Iron sulphide will be formed.

16. Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.

Solution

In a suspension, the particle size is larger than those in a colloidal solution. Also in a suspension, the molecular interaction is not strong enough to keep the particles suspended and hence they settle down.

17. Smoke and fog both are aerosols. In what way are they different?

Solution

Gas forms the dispersion medium for both fog and smoke. The only difference is that the dispersed phase in fog is liquid while in case of smoke it is a solid.

18. Classify the following as physical or chemical properties :
(i) The composition of a sample of steel is : 98% iron, 1.5% carbon and 0.5% other elements.
(ii) Zinc dissolves in hydrochloric acid with the evolution of hydrogen gas.
(iii) Metallic sodium is soft enough to be cut with a knife.
(iv) Most metal oxides form alkalis on interacting with water.

Solution

(i) Composition of a sample of steel is 98% iron, 1.5% carbon and 0.5% other elements. It is a chemical property as no new compound is formed. Steel is an alloy.

(ii) Zinc reacts with HCl to give out zinc chloride and hydrogen gas hence it is chemical property.

(iii) Cutting metallic sodium with knife will not involve any chemical reaction. Also, no new compounds are formed hence it is a physical property.

(iv) A new compound is form by the interaction of metal oxides with alkalis hence it is chemical property.

19. The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare a 50%. (mass by volume)
solution of sodium hydroxide (NaOH). ‘A’ dissolved 50 g of NaOH in 100 ml of water, ‘B’ dissolved 50 g
of NaOH in 100 g of water while ‘C’ dissolved 50 g of NaOH in water to make 100 ml of solution. Which one of them has made the desired solution and why?

Solution

Student ‘C’ has made the desired solution.

20. Name the process associated with the following:
(i) Dry ice is kept at room temperature and at one atmospheric pressure.
(ii) A drop of ink placed on the surface of water contained in a glass spreads throughout the water.
(iii) A potassium permanganate crystal is in a beaker and water is poured into the beaker with stirring.
(iv) A acetone bottle is left open and the bottle becomes empty.
(v) Milk is churned to separate cream from it.
(vi) Settling of sand when a mixture of sand and water is left undisturbed for some time.
(vii) Fine beam of light entering through a small hole in a dark room, illuminates the particles in its paths.

Solution

(i) Sublimation
(ii) Diffusion
(iii) Dissolution/diffusion
(iv) Evaporation, diffusion
(v) Centrifugation
(vi) Sedimentation
(vii) Tyndall effect (Scattering of light)

21. You are given two samples of water, labelled as ‘A’ and ‘B’. Sample ‘A’ boils at 100°C and sample ‘B’ boils at 102°C. Which sample of water will not freeze at 0°C? Comment.

Solution

Sample ‘B’ is not pure water and hence it will not freeze at 0°C. At a pressure of 1 atm, the boiling point of pure water is 100°C and the freezing point of pure water is 0°C.

22. What are the favourable qualities given to gold when it is alloyed with copper or silver for the purpose of making ornaments?

Solution

Pure gold (24 karats) is very soft and it does not have enough strength. Silver and copper are alloyed with gold, to give it strength. 24 karat gold is an alloy that has 20 parts of gold and 4 parts of silver.

23. An element is sonorous and highly ductile. Under which category would you classify this element? What other characteristics do you expect the element to possess?

Solution

The element is a metal. Other characteristics possessed by the element are:

• Lustre
• Malleability
• Heat
• Electrical conductivity

24. Give an example each for the mixture having the following characteristics. Suggest a suitable method to separate the components of these mixtures.
(i) A volatile and a non-volatile component.
(ii) Two volatile components with appreciable difference in boiling points.
(iii) Two immiscible liquids.
(iv) One of the components changes directly from solid to gaseous state.
(v) Two or more coloured constituents soluble in some solvent.

Solution

(i) Mixture of acetone and water can be separated by distillation.

(ii) Mixture of petrol and kerosene can be separated by distillation.

(iii) Mixture of oil and water can be separated by fractional distillation.

(i)v Separating naphthalene by filtration and then separation of ammonium chloride from water by evaporation.

(v) Mixture of pigments from a flower petal extract can be separated by chromatography.

25. Fill in the blanks
(i) A colloid is a _____ mixture and its components can be separated by the technique known as_____
(ii) Ice, water and water vapour look different and display different _____ properties but they are_____ the same.
(iii) A mixture of chloroform and water taken in a separating funnel is mixed and left undisturbed for some time. The upper layer in the separating funnel will be of _____ and the lower layer will be that of _____
(iv) A mixture of two or more miscible liquids, for which the difference in the boiling points is less than 25K can be separated by the process called _____
(v) When light is passed through water containing a few drops of milk, it shows a bluish tinge. This is due to the _____ of light by milk and the phenomenon is called _____ This indicates that milk is a _____ solution.

Solution

(i) A colloid is a heterogeneous mixture and its components can be separated by the technique known as centrifugation.

(ii) Ice, water and water vapour look different and display different physical properties but they are chemically the same. 

(iii) A mixture of chloroform and water taken in a separating funnel is mixed and left undisturbed for some time. The upper layer in the separating funnel will be of water and the lower layer will be that of chloroform.

(iv) A mixture of two or more miscible liquids, for which the difference in the boiling points is less than 25 K can be separated by the process called fractional distillation.

(v) When light is passed through water containing a few drops of milk, it shows a bluish tinge. This is due to the scattering of light by milk and the phenomenonis called Tyndall effect. This indicates that milk is a colloidal solution.

26. Sucrose (sugar) crystals obtained from sugarcane and beetroot are mixed together. Will it be a pure substance or a mixture? Give reasons for the same.

Solution

As the chemical composition of sugar crystals remains the same irrespective of its source, the mixture is a pure substance.

27. Give some examples of Tyndall effect observed in your surroundings.

Solution

When light passes through a heterogeneous mixture, Tyndall effect can be seen. Example, when sunlight passes through the canopy of a dense forest.

28. Can we separate alcohol dissolved in water by using a separating funnel? If yes, then describe the procedure. If not, explain.

Solution

Alcohol dissolved in water cannot be separated by separating funnel because both are miscible solvents.

29. On heating calcium carbonate gets converted into calcium oxide and carbon dioxide.
(i) Is this a physical or a chemical change?
(ii) Can you prepare one acidic and one basic solution by using the products formed in the above process?
If so, write the chemical equation involved.

Solution

(i) It is a chemical change Calcium carbonate → Calcium oxide + Carbon dioxide
CaCO₃ → CaO + CO₂
(ii) Acidic and basic solutions can be prepared by dissolving the products of the above process in water
CaO + H₂O → Ca(OH)₂ (basic solution)
CO₂ + H₂O → H₂CO₃(acidic solution)

30. Non-metals are usually poor conductors of heat and electricity. They are non-lustrous, non-sonorous, non-malleable and are coloured.
(a) Name a lustrous non-metal.
(b) Name a non-metal which exists as a liquid at room temperature.
(c) The allotropic form of a non-metal is a good conductor of electricity. Name the allotrope.
(d) Name a non-metal which is known to form the largest number of compounds.
(e) Name non-metals other than carbon which show allotropy.
(f) Name a non-metal which is required for combustion.

Solution

(a) Iodine
(b) Bromine
(c) Graphite
(d) Carbon
(e) Sulphur, Phosphorus
(f) Oxygen

31. Classify the substances given in figure into elements and compounds :

Cu

Sand

H2O

CaCO3

O3

Zn

NaCl(aq)

F2

Hg

Diamond(C)

Wood

Solution 

Elements	Compounds
Cu	CaCO3
Zn	H2O
F2
O2
Diamond (c)
Hg

32. Which of the following are not compound?
(a) Chlorine gas
(b) Potassium chloride
(c) Iron
(d) Iron sulphate
(e) Aluminium
(f) Iodine
(g) Carbon
(h) Carbon monoxide
(i) Sulphur powder

Solution

Chlorine gas, iron, aluminium, iodine, carbon and sulphur powder are not compounds.

Long Answer Questions

33. Fractional distillation is suitable for separation of miscible liquids with a boiling point difference of about 25 K or less. What part of fractional distillation apparatus makes it efficient and possess an advantage over a simple distillation process. Explain using a diagram.

Solution

The most important part of fractional distillation apparatus is the fractionating column. It has glass beads in it. This prevents the upward movement of the vapours of the two liquids. The vapours of the liquid having high boiling point get condensed earlier at the lower levels of the column. The latent heat released helps to take the vapours of low boiling liquid to a greater height in the fractionating column.

The advantages of fractional distillation are as follows:

1. The liquids with a boiling point difference of about or less than 25 K can be separated by this method.
2. Both evaporation and condensation take place simultaneously during the process.
3. A mixture (like petroleum) which contains several components can also be separated by this process.

34. (i) Under which category of mixtures will you classify alloys and why?
(ii) A solution is always a liquid. Comment.
(iii) Can a solution be heterogeneous?

Solution

(i) An alloy is a homogenous mixture of two or more elements. The constituent elements of an alloy can be two metals or a metal with a non-metal. An alloy is classified as a homogenous mixture as it exhibits the properties of its constituent elements.

Examples: Brass is an alloy which shows characteristics of copper and Zinc and their composition vary from 20 to 35 %.

(ii) The solutions are usually liquids, but not always. Solutions can also include a mixture of two solids like in alloys, and a mixture of gases, such as air.

(iii) Yes, solutions can be heterogeneous also.

35. Iron filings and sulphur were mixed together and divided into two parts, ‘A’ and ‘B’. Part ‘A’ was heated strongly, while part ‘B’ was not heated. Dilute hydrochloric acid was added to both the parts and evolution of gas was seen in both the cases. How will you identify the gases evolved?

Solution

Part A
When iron fillings and sulphur is heated it will give following reaction

Part B

Fe (s) + S (s)→ Mixture of iron filings and sulphur
When dilute HCl is added to it
Fe (s) + S (s) + 2 HCl (aq) → FeCl₂+ H₂ gas
Sulphur remains unreacted.H2S gas formed has a foul smell and on passing through lead acetate solution, it turns the solution black. Hydrogen gas burns with a pop sound.

36. A child wanted to separate the mixture of dyes constituting a sample of ink. He marked a line by the ink on the filter paper and placed the filter paper in a glass containing water as shown in fig. The filter paper was removed when the water moved near the top of the filter paper.

(i) What would you expect to see, if the ink contains three different coloured components?
(ii) Name the technique used by the child.
(iii) Suggest one more application of this technique.

Solution

(i) Three different bands are observed on the paper if the ink contains three different coloured components.

(ii) Child uses the technique of paper chromatography.

(iii) The different pigments present in the chlorophyll can be separated by paper chromatography.

37. A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/ tumbler in the box as shown in the fig. They were amazed to see that milk taken in the tumbler was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it.

(a) Explain why the milk sample was illuminated. Name the phenomenon involved.
(b) Same results were not observed with a salt solution. Explain.
(c) Can you suggest two more solutions which would show the same effect as shown by the milk solution?

Solution

(a) Milk is a colloidal substance. The particulate matter present in the milk scatter the light scatter thereby resulting in Tyndall effect. Because of this, the milk gets illuminated.

(b) Salt solution is a homogenous solution. Small particles present in salt solution do not scatter light. This is the reason why there is no Tyndall effect in salt solution. The salt solution does not get illuminated as it does not exhibit the Tyndall effect.

(c) Detergent solution and sulphur solution will exhibit the Tyndall effect.

38. Classify each of the following, as a physical or a chemical change. Give reasons.
(i) Drying of a shirt in the Sun.
(ii) Rising of hot air over a radiator.
(iii) Burning of kerosene in a lantern.
(iv) Change in the colour of black tea on adding lemon juice to it.
(v) Churning of milk cream to get butter.

Solution

(i) There is no chemical reaction or any chemical changed involved in drying a shirt in the sun, hence it is a physical phenomenon.

(ii) In a radiator water is converted to vapours. Hot air being lighter rises upwards. Thus, rising of hot air over radiator is a physical change.

(iii) Kerosene burns by using the atmospheric oxygen and produces carbon dioxide, this is the reason why burning of kerosene in a lantern is a chemical change.

(iv) Lemon juice is a source of citric acid, ascorbic acid and malic acid. These acids react with the flavin antioxidants present in black tea and change the colour of the tea. Thus, the change in the colour of black tea on adding lemon juice is a chemical change.

(v) There is no chemical reaction taking place when milk is churned to make butter. This is the reason why churning of milk cream to get butter is a physical change.

39. During an experiment, the students were asked to prepare a 10% (Mass/Mass) solution of sugar in water. Ramesh dissolved 10 g of sugar in 100 g of water while Sarika prepared it by dissolving 10 g of sugar in water to make 100 g of the solution.
(i) Are the two solutions of the same concentration?
(ii) Compare the mass % of the two solutions.

Solution 

(i) The two solutions are not of the same concentration.

(b) Solution prepared by Ramesh:

40. You are provided with a mixture containing sand, iron filings, ammonium chloride and sodium chloride.
Describe the procedures you would use to separate these constituents from the mixture.

Solution

The procedures to be used to separate the constituents from the mixture are:

• Step-1:With the help of a magnet separate iron filings.
• Step-2:Sublimation of the remaining mixture separates ammonium chloride.
• Step-3:Add water to the remaining mixture, stir and filter.
• Step-4:The filtrate can be evaporated to get back sodium chloride.

41. Arun has prepared 0.01% (by mass) solution of sodium chloride in water. Which of the following correctly represents the composition of the solutions?
(i) 1.00 g of NaCl + 100 g of water
(ii) 0.11 g of NaC1 + 100 g of water
(iii) 0.01 g of NaC1 + 99.99 g of water
(iv) 0.10 g of NaC1 + 99.90 g of water

Solution

Option (iii) correctly represents the composition of the solutions.

42. Calculate the mass of sodium sulphate required to prepare its 20% (mass percent) solution in 100 g of water.

Solution

In a 20% solution containing 100 g water; the mass percentage of water = 100 — 20 = 80%
80% of solution is 100 gram
100% of solution is 100/80 gram
20% of solution is 100/80 × 20 = 25 gram
Hence, to prepare 20% (w/w) solution in 100 gram of water 25 gram of sodium sulphate is needed.

1. Which of the following correctly represents 360 g of water?
(i) 2 moles of H₂O
(ii) 20 moles of water
(iii) 6.022 × 10²³ molecules of water

(iv) 1.2044 × 10²⁵ molecules of water

(a) (i)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)

Solution

(d) (ii) and (iv)

Number of moles = Mass of water/Molar mass of water

Number of moles = 360/120 = 20

Number of molecules = 20 ×6.022× 10²³
= 1.2044 ×10²⁵ molecules of water

2. Which of the following statements is not true about an atom?
(a) Atoms are not able to exist independently.
(b) Atoms are the basic units from which molecules and ions are formed.
(c) Atoms are always neutral in nature.
(d) Atoms aggregate in large numbers to form the matter that we can see, feel or touch.

Solution

(a) Atoms are not able to exist independently.

3. The chemical symbol for nitrogen gas is :
(a) Ni
(b) N₂
(c) N⁺
(d) N

Solution

(b) N₂

4. The chemical symbol for sodium is :
(a) So
(b) Sd
(c) NA
(d) Na

Solution

(d) Na

Sodium word is derived from Latin word Natrium hence the chemical name of sodium is Na.

5. Which of the following would weigh the highest?
(a) 0.2 mole of sucrose (C₁₂ H₂₂ O₁₁)
(b) 2 moles of CO₂
(c) 2 moles of CaCO₃
(d) 10 moles of H₂O

Solution

(c) 2 moles of CaCO₃

6. Which of the following has maximum number of atoms ?
(a) 18g of H₂O
(b) 18g of O₂
(c) 18g of CO₂
(d) 18 g of CH₄

Solution

(d) 18 g of CH₄

7. Which of the following contains maximum number of molecules ?
(a) 1 g CO₂
(b) 1 g N₂
(c) 1 g H₂
(d) 1 g CH₄

Solution

(c) 1 g H₂

1 g of H₂ = ½ ×N_A
= 0.5 N_A
= 0.5 × 6.022 × 10²³
= 3.011 × 10²³

8. Mass of one atom of oxygen is :
(a) 16/(6.023 × 10²³ g)
(b) 32/(6.023 × 10²³ g)
(c) 1/(6.023 × 10²³ g)
(d) 8u

Solution

(a) 16/(6.023 ×10²³ g)

Mass of one atom of oxygen = Atomic mass/N_A

= 16/6.023× 10²³ g

9. 3.42 g of sucrose are dissolved in 18 g of water in a beaker. The number of oxygen atoms in the solution are :
(a) 6.68 × 10²³
(b) 6.09 × 10²²
(c) 6.022 × 10²³
(d) 6.022 × 10²¹

Solution

(a) 6.68 × 10²³

1 mol of sucrose (C₁₂H₂₂O₁₁) contains = 11× N_A atoms of oxygen,

Here, N_A= 6.023×10²³

0.01 mol of sucrose (C₁₂H₂₂O₁₁) contains = 0.01 × 11 × N_A atoms of oxygen

= 0.11× N_A atoms of oxygen

= 18 g/(1×2+ 16)gmol^-1

= 1mol

1mol of water (H₂O) contains 1× N_A atom of oxygen

Total number of oxygen atoms = Number of oxygen atoms from sucrose + Number of oxygen atoms from water

= 0.11 N_A + 1.0 N_A = 1.11N_A

Number of oxygen atoms in solution = 1.11 × Avogadro’s number

= 1.11 × 6.022 ×10²³

= 6.68 × 10²³

10. A change in the physical state can be brought about :
(a) Only when energy is given to the system.
(b) Only when energy is taken out from the system.
(c) When energy is either given to, or taken out from the system.
(d) Without any energy change.

Solution

(c) When energy is either given to, or taken out from the system.

Short Answer Questions

11. Which of the following represents a correct chemical formula? Name it.
(a) CaCl
(b) BiPO₄
(c) NaSO₄
(d) NaS

Solution

(a) CaCl = Wrong (valency of Ca = 2, Cl = 1)
(b) BiPO₄ = Correct (valency of Bi = 3, PO₄ = 3)
(c) NaSO₄ = Wrong (valency of Na = 1, SO₄ = 2)
(d) NaS = Wrong (valency of Na = 1, Sulphide = 2)

Bismuth phosphate is right because both ions are trivalent.

12. Write the molecular formulae for the following compounds.

Solution

(a) Copper (II) bromide = CuBr₂

(b) Aluminium (III) nitrate = Al(NO₃)₃

(c) Calcium (II) phosphate = Ca₃(PO₄)₂

(d) Iron (III) sulphide = Fe₂S₃

(e) Mercury (II) chloride = HgCl₂

(f) Magnesium (II) acetate = Mg(CH₃COO)₂

13. Write the molecular formulae of all the compounds that can be formed by the combination of given ions : Cu³⁺, Na⁺, Fe³⁺, Cl, SO³₄ PO₄³ .

Solution

CuCl₂/CuSO₄/Cu₃(PO₄)

NaCl/Na₂SO₄/Na₃PO₄

FeCl₃/Fe(SO₄)₃/FePO₄

14. Write the cations and anions present (if any) in the following compounds :
(a) CH₃COONa
(b) NaCl
(c) H₂
(d) NH₄NO₃

Solution

1. Which of the following correctly represent the electronic distribution in the Mg atom?
(a) 3, 8, 1
(b) 2, 8, 2
(c) 1, 8, 3
(d) 8, 2, 2

Solution

(b) 2, 8, 2

Atomic number of Mg is 12.Therefore the electronic distribution will be 1s²2s²2p⁶3s².

2. Rutherford’s ‘alpha (a ) particles scattering experiment’ resulted in to discovery of :
(a) Electron
(b) Proton
(c) Nucleus in the atom
(d) Atomic mass

Solution

(c) Nucleus in the atom

Rutherford’s ‘alpha (α) particles scattering experiment’ showed that few alpha particles returned to their original path. This showed the presence of nucleus in the centre.

3. The number of electrons in an element X is 15 and the number of neutrons is 16. Which of the following is the correct representation of the element?
(a) ₁₅X³¹
(b) ₁₆X³¹
(c) ₁₅X¹⁶
(d) ₁₆X¹⁵

Solution

(a) ₁₅X³¹

Atomic number is the number of protons in an element. Number of protons and electrons are equal in an element. The atomic number is written as a subscript and the mass number is written as the superscript of the element.

4. Dalton’s atomic theory successfully explained :
(i) Law of conservation of mass
(ii) Law of constant composition
(iii) Law of radioactivity
(iv) Law of multiple proportions
(a) (i), (ii) and (iii)
(b) (i), (iii) and (iv)
(c) (ii), (iii) and (iv)
(d) (i), (ii) and (iv)

Solution

(d) (i), (ii) and (iv)

Dalton’s theory explains the Law of conservation of mass, Law of constant composition, Law of multiple proportion.

5. Which of the following statements about Rutherford’s model of atom are correct?
(i) considered the nucleus as positively charged
(ii) established that the a-particles are four times heavy as a hydrogen atom
(iii) can be compared to solar system
(iv) was in agreement with Thomson’s model
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) Only (i)

Solution

(a) (i) and (iii)

The positively charged alpha particles were deflected by the nucleus. This indicates that the nucleus is positively charged. Rutherford also postulated that electrons are arranged in an atom around the nucleus like planets arranged around sun.

6. Which of the following are true for an element?
(i) Atomic number = number of protons + number of electrons
(ii) Mass number = number of protons + number of neutrons
(iii) Atomic mass = number of protons = number of neutrons
(iv) Atomic number = number of protons = number of electrons
(a) (i) and (ii)
(b) (i) and (iii)
(c) and (iii)
(d) (ii) and (iv)

Solution

(d) (ii) and (iv)

Atomic number Z is the number of proton present in an atom. This is also equal to number of electrons in an atom. As the mass of neutron is negligible, number of protons and electron are added to obtain mass number of an element.

7. In the Thomson’s model of atom, which of the following statements are correct?
(i) The mass of the atom is assumed to be uniformly distributed over the atom.
(ii) The positive charge is assumed to be uniformly distributed over the atom.
(iii) The electrons are uniformly distributed in the positively charged sphere.
(iv) The electrons attract each other to stabilise the atom.
(a) (i), (ii) and (iii)
(b) (i) and (iii)
(c) (i) and (iv)
(d) (i), (iii) and (iv)

Solution

(a) (i), (ii) and (iii)

Thomson proposed that negatively charged electron are stabilised by positively charged protons in the nucleus.

8. Rutherford’s a -particle scattering experiment showed that :
(i) Electrons have negative charge.
(ii) The mass and positive charge of the atom is concentrated in the nucleus.
(iii) Neutron exists in the nucleus.
(iv) Most of the space in atom is empty. Which of the above statements are correct?
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (iv)
(d) (iii) and (iv)

Solution

(b) (ii) and (iv)

9. The ion of an element has 3 positive charges. Mass number of the atom is 27 and the number of neutrons is 14. What is the number of electrons in the ion?
(a) 13
(b) 10
(c) 14
(d) 16

Solution

(b) 10

Mass number (A) of the atom = 27
Number of neutron in the atom =14
Number of electrons = Mass number - Number of neutrons
= 27-14 = 13
Since ions of the element has 3 positive charges number of electron in the ion is 13-3 which equal 10.

10. Identify the Mg²⁺ ion from the fig. where, n and p represent the number of neutrons and protons respectively :

11. In a sample of ethyl ethanoate (CH₃COOC₂H₅), the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?
(a) One of the oxygen atoms has gained electrons.
(b) One of the oxygen atoms has gained two neutrons.
(c) The two oxygen atoms are isotopes.
(d) The two oxygen atoms are isobars.

Solution

(c) The two oxygen atoms are isotopes.

Two oxygen atoms in CH₃COOC₂H₅ can have different number of neutrons only if the two O-atoms are isotopes. Isotopes of an element have same number of protons (and electrons) but different number of neutrons.

12. Elements with valency 1 are :
(a) Always metals
(b) Always metalloids
(c) Either metals or non-metals
(d) Always non-metals

Solution

(c) Either metals or non-metals

If an element shows positive valency then it is a metal and if it shows negative valency then it is a non-metal.

13. The first model of an atom was given by :
(a) N. Bohr
(b) E. Goldstein
(c) Rutherford
(d) J.J. Thomson

Solution

(d) J.J. Thomson

14. An atom with 3 protons and 4 neutrons will have a valency of :
(a) 3
(b) 7
(c) 1
(d) 4

Solution

(c) 1

15. The electron distribution in an aluminium atom is :
(a) 2, 8, 3
(b) 2, 8, 2
(c) 8, 2, 3
(d) 2, 3, 8

Solution

(a) 2, 8, 3

Atomic number of Aluminium is 13. Therefore, the first shell can have maximum of 2 electrons and the second shell holds a maximum of 8 electrons.

16. Which of the following fig. do not represent Bohr’s model of an atom correctly?

(a) (i) and (ii)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (i) and (iv)

Solution

(c) (ii) and (iv)

First shell can have a maximum of 2 electrons and the second shell can have a maximum of 8 electrons.

17. Which of the following statement is always correct?
(a) An atom has equal number of electrons and protons.
(b) An atom has equal number of electrons and neutrons.
(c) An atom has equal number of protons and neutrons.
(d) An atom has equal number of electrons, protons and neutrons.

Solution

(a) An atom has equal number of electrons and protons.

In an atom the number of protons is always equal to number of electrons.

18. Atomic models have been improved over the years. Arrange the following atomic models in the order of their chronological order :

(i) Rutherford’s atomic model,

(ii) Thomson’s atomic model,

(iii) Bohr’s atomic model.
(a) (i), (ii) and (iii)
(b) (ii), (iii) and (i)
(c) (ii), (i) and (iii)
(d) (iii), (ii) and (i)

Solution

(c) (ii), (i) and (iii)

Short Answer Questions

19. Is it possible for the atom of an element to have one electron, one proton and no neutron? If so, name the element.

Solution

Yes, Hydrogen is the element which has only 1 proton and 1 electron and no neutron. Therefore there is no repulsive force in the nucleus and hence it is stable.
1 proton means atomic no. (Z) = 1
1 neutron means mass no. (A) = p + n = 1 + 1 = 2
1 electron and 1 proton mean that atom is electrically neutral.
Hence, the element is ₁¹H (An isotop of Hydrogen – Deuterium)

20. Write any two observations which support the fact that atoms are divisible.

Solution

1. Discovery of electrons and protons support the fact that atoms are divisible.
2. During a chemical reaction, there is either transfer or sharing of electrons which leads to the rearrangement of electrons in the atom.

21. Will ₃₅Cl and ₃₇Cl have different valencies? Justify your answer.

Solution

No, ₃₅Cl and ₃₇Cl both are the isotopes of the same element hence they cannot have different valencies.
Both atoms have valency 1.

22. Why did Rutherford select a gold foil in his a-ray scattering experiment?

Solution

Gold is the most malleable metal and Rutherford wanted the thinnest layer. Therefore, Rutherford used gold for his scattering experiment as it is a heavy metal with high atomic number and it is highly malleable.

23. Find out the valency of the atoms represented by the fig. (a) and (b).

Solution

As atom (a) has 8 electron in its valence shell, it has zero valency.

Atom (b) has a valency of +1 as it has 7 electrons in it outermost shell. To achieve the octet configuration, atom (b) will accept 1 electron.

24. One electron is present in the outermost shell of the atom of an element X. What would be the nature and value of charge on the ion formed if this electron is removed from the outermost shell?

Solution

A cation is formed if an electron is removed from the outermost shell and the charge of the element will be +1.

25. Write down the electron distribution of chlorine atom. How many electrons are there in the L shell? (Atomic number of chlorine is 17.)

Solution

Atomic number of chlorine atom = 17

So, its electronic configuration is
¹⁷Cl = K-2, L-8, M-7

26. In the atom of an element X, 6 electrons are present in the outermost shell. If it acquires noble gas configuration by accepting requisite number of electrons, then what would be the charge on the ion so formed?

Solution

6 electrons are already present in the outermost orbital. In order to attain noble gas configuration the element has to accept two electrons. Therefore, the charge on an atom of element X is -2.

27. What information do you get from the fig. about the atomic number, mass number and valency of atoms X, Y and Z? Give your answer in a tabular form.

Solution

Sl. No.	Atomic number	Mass number	Valency
X	5	11	3
Y	8	18	2
Z	15	31	3, 5

28. In response to a question, a student stated that in an atom, the number of protons is greater than the number of neutrons, which in turn is greater than the number of electrons. Do you agree with the statement? Justify your answer.

Solution

The statement is incorrect. In a neutral atom the number of protons and electrons is always equal. Number of neutron can be greater than the number of electron. Number of neutron can be equal to or greater than the number of protons because mass number is equal to double the atomic number.

29. Calculate the number of neutrons present in the nucleus of an element X which is represented as ₁₅³¹X.

Solution

Mass number = No. of protons + No. of neutrons = 31
∴ Number of neutrons = 31–number of protons
= 31–15
= 16

30. Match the names of the scientists given in column A with their contributions towards the understanding of the atomic structure as given in column B :

	Column A		Column B
(a)	Ernest Rutherford	(i)	Indivisibility of atoms
(b)	J.J. Thomson	(ii)	Stationary orbits
(c)	Dalton	(iii)	Concept of nucleus
(d)	Neils bohr	(iv)	Discovery of electrons
(e)	James Chadwick	(v)	Atomic number
(f)	E. Goldstein	(vi)	Neutron
(g)	Mosley	(vii)	Canal rays

Solution

(a)	Ernest Rutherford	Concept of nucleus
(b)	J.J. Thomson	Discovery of electrons
(c)	Dalton	Indivisibility of atoms
(d)	Neils Bohr	Stationary orbits
(e)	James Chadwick	Neutron
(f)	E. Goldstein	Canal rays
(g)	Mosley	Atomic number

31. The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?

Solution

Isobars are elements with different atomic numbers but same mass numbers. Calcium and argon are isobars.

32. Complete the table on the basis of information available in the symbols given below :
(a) ₁₇Cl³⁵ (b) ₆C¹² (c) ₃₅Br⁸⁵

Solution

Elements	No. of protons	No. of neutrons
17Cl35	17	35 – 17 = 18
6C12	6	12 – 6 = 6
35Br85	35	81 – 35 = 46

33. Helium atom has 2 electrons in its valence shell but its valency is not 2. Explain.

Solution

As Helium atom has 2 electrons in its outermost shell, its duplet is complete. Therefore the valency is zero.

34. Fill in the blanks in the following statements :
(a) Rutherford’s a -particle scattering experiment led to the discovery of the _____.
(b) Isotopes have same _____ but different _____.
(c) Neon and chlorine have atomic numbers 10 and 17 respectively. Their valencies will be _____ and _____ respectively.
(d) The electronic configuration of silicon is _____ and that of sulphur is _____.

Solution

(a) nucleus
(b) same atomic numbers, mass numbers
(c) 0 and –1
(d) Si = 2,8,4 and S = 2,8,6

35. An element X has a mass number 4 and atomic number 2. Write the valency of this element?

Solution

As the K shell is completely filled, valency is zero.

Long Answer Questions

36. Why do helium, neon and argon have a zero valency?

Solution

Helium has two electrons in its only energy shell, while Argon and Neon have 8 electrons in their valence shells. These elements do not have any tendency to combine with other elements as they have maximum number of electrons in their valence shells. Therefore, they have zero valency.

37. The ratio of the radii of hydrogen atom and its nucleus is ~ 10⁵. Assuming the atom and the nucleus to be spherical,

(i) what will be the ratio of their sizes?

(ii) If atom is represented by planet earth ‘R_e’ = 6.4 ×10⁶m, estimate the size of the nucleus.

Solution

(i) Volume of the sphere = 4/3 πr³

Let R be the radius of the atom and r be that of the nucleus.

Therefore ,R = 10⁵r

(ii) If the atom is represented by the planet earth (R_e = 6.4×10⁶m) then the radius of the nucleus would be

38. Enlist the conclusions drawn by Rutherford from his a-ray scattering experiment.

Solution

The following conclusions were made from the Rutherford α-particle scattering experiment:

1. As most of the α-particles passed through the gold foil undeflected, most of the space inside the atom is empty.
2. Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.
3. A very small fraction of α-particles were deflected by 180°,indicating that all the positive charges and mass of the gold atom were concentrated in a very small volume within the atom.

From the data he also calculated that the radius of the nucleus is about 105 times less than the radius of the atom.

39. In what way is the Rutherford’s atomic model different from that of Thomson’s atomic model?

Solution

Rutherford’s atomic model proposed that the electrons revolve around the nucleus in well-defined orbits. The center of the atom is positively charged and is called the nucleus. The model also proposed that the size of the nucleus is very small as compared to the size of the atom and nearly the entire mass of an atom is centred in the nucleus.

Thomson’s model of an atom was similar to that of a christmas pudding. The electrons are studded like currants in a positively charged sphere like christmas pudding and the mass of the atom was supposed to be uniformly distributed.

40. What were the drawbacks of Rutherford’s model of an atom?

Solution

Rutherford’s model failed to explain the stability of the atom. Any particle in a circular orbit would undergo an acceleration and the charged particles would radiate energy. Thus, the revolving electron would lose energy and finally fall into the nucleus. In other words, the atom should collapse.

41. What are the postulates of Bohr’s model of an atom?

Solution

The postulates of Neils Bohr’s about the model of an atom are as follows:

1. Only certain special orbits known as discrete orbits of electrons, are allowed inside the atom.
2. While revolving in discrete orbits the electrons do not radiate energy.

These orbits are called energy levels. Energy levels in an atom are shown by circles. These orbits are represented by the letters K,L,M,N,... or the numbers, n=1,2,3,4,....

42. Show diagrammatically the electron distributions in a sodium atom and a sodium ion and also give their atomic number.

Solution

As the atomic number of sodium atom is 11, it has 11 electrons. A positively charged sodium ion (Na⁺) is formed by the removal of one electron from a sodium atom. Thus, a sodium ion has 11–1 = 10 electrons. The electronic configuration of sodium ion will be 2, 8. The atomic number of an element is equal to the number of protons in its atom. As, sodium atom and sodium ion have the same number of protons, therefore, the atomic number of both is 11.

43. In the Gold foil experiment of Geiger and Marsden, that paved the way for Rutherford’s model of an atom, ~ 1.00% of the α-particles were found to deflect at angles > 50º. If one mole of α-particles were bombarded on the gold foil, compute the number of α-particles that would deflect at angles less than 500.

Solution

% of α-particles deflected more than 50°=1% of α-particles.

% of α-particles deflected less than 50° = 100–1% =  99%

Number of α-particles bombarded = 1 mole = 6.022×10²³ particles

Number of particles that deflected at an angle less than 50°

1. Which of the following can be made into crystal?
(a) A bacterium
(b) An amoeba
(c) A virus
(d) A sperm

Solution

(c) A virus

Viruses are considered to be intermediates between living and non-living. This is because they cannot metabolize or reproduce on their own. Moreover, virus requires a host for all its processes. Viruses can be stored as crystal like chemicals. Virus crystals are collection of millions of virus cells.

2. A cell will swell up if :
(a) The concentration of water molecules in the cell is higher than the concentration of water molecules in surrounding medium.
(b) The concentration of water molecules in surrounding medium is higher than water molecules concentration in the cell.
(c) The concentration of water molecules is same in the cell and in the surrounding medium.
(d) Concentration of water molecules does not matter.

Solution

(b) The concentration of water molecules in surrounding medium is higher than water molecules concentration in the cell.
The water from the surrounding enter the cell through osmosis and the cell swells up when the concentration of water molecules in surrounding medium is higher.

3. Chromosomes are made up of :
(a) DNA
(b) protein
(c) DNA and protein
(d) RNA

Solution

(c) DNA and protein

4. Which of these options are not a function of ribosomes?
(i) It helps in manufacture of protein molecules
(ii) It helps in manufacture of enzymes
(iii) It helps in manufacture of hormones
(iv) It helps in manufacture of starch molecules
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (iv) and (i)

Solution

(c) (iii) and (iv)

Proteins are produced in ribosomes. Enzymes are proteins. Hormones and starch are not produced in ribosome.

5. Which of these is not related to endoplasmic reticulum?
(a) It behaves as transport channel for proteins between nucleus and cytoplasm.
(b) It transports materials between various regions in cytoplasm.
(c) It can be the site of energy generation.
(d) It can be the site for some biochemical activities of the cell.

Solution

(c) It can be the site of energy generation.

Energy is produced in the mitochondria.

6. Following are a few definitions of osmosis, read carefully and select the correct definition :
(a) Movement of water molecules from a region of higher concentration to a region of lower concentration through a semipermeable membrane.
(b) Movement of solvent molecules from its higher concentration to lower concentration.
(c) Movement of solvent molecules from higher concentration to lower concentration of solution through a permeable membrane.
(d) Movement of solute molecules from lower concentration to higher concentration of solution through a semipermeable membrane.

Solution

(a) Movement of water molecules from a region of higher concentration to a region of lower concentration through a semipermeable membrane.

7. Plasmolysis in a plant cell is defined as :
(a) Break down (lysis) of plasma membrane in hypotonic medium
(b) Shrinkage of cytoplasm in hypertonic medium
(c) Shrinkage of nucleoplasm
(d) None of the above

Solution

(b) Shrinkage of cytoplasm in hypertonic medium

Living plant cell loses water through the process of osmosis. This results in shrinking or contraction of the contents of the cell away from the cell wall. This is known as plasmolysis. When a plant cell has more water content than the surrounding, the plant cell tends to transfer water to its surroundings.

8. Which of the following are covered by a single membrane?
(a) Mitochondria
(b) Vacuole
(c) Lysosome
(d) Plastid

Solution

(b) Vacuole, (c) Lysosome

Both (b) and (c)
Both vacuole and lysosome are single membrane bound cell organelles. Mitochondria and plastids are double membrane bound cell organelles

9. Find out the false sentences :
(a) Golgi apparatus is involved with the formation of lysosomes.
(b) Nucleus, mitochondria and plastid have DNA; hence, they are able to make their own structural proteins.
(c) Mitochondria is said to be the powerhouse of the cell as ATP is generated in them.
(d) Cytoplasm is called as protoplasm.

Solution

(a) Golgi apparatus is involved with the formation of lysosomes.

Golgi apparatus has a role in the storage and synthesis of certain biomolecules. It does not have any role in the synthesis of lysosome.

10. Find out the correct sentence :
(a) Enzymes packed in lysosomes are made by RER (rough endoplasmic reticulum).
(b) Rough endoplasmic reticulum and smooth endoplasmic reticulum produce lipid and protein respectively.
(c) Endoplasmic reticulum is related with the destruction of plasma membrane.
(d) Nucleoid is present inside the nucleoplasm of eukaryotic nucleus.

Solution

(a) Enzymes packed in lysosomes are made by RER (rough endoplasmic reticulum).

RER has ribosomes present on its surface. These ribosomes are responsible for the synthesis of proteins and enzymes.

11. Which cell organelle plays a crucial role in detoxifying many poisons and drugs in a cell?
(a) Golgi apparatus
(b) Lysosomes
(c) Smooth endoplasmic reticulum
(d) Vacuoles

Solution

(c) Smooth endoplasmic reticulum

SER plays an important role in detoxifying many poisons and drugs in the liver cells of vertebrates.

12. The proteins and lipids, essential for building the cell membrane, are manufactured by :
(a) rough endoplasmic reticulum
(b) golgi apparatus
(c) plasma membrane
(d) mitochondria

Solution

(a) rough endoplasmic reticulum

Endoplasmic reticulum plays important role in the production of both lipids and proteins. SER produces proteins and RER produces lipids.

13. The undefined nuclear region of prokaryotes are also known as :
(a) nucleus
(b) nucleolus
(c) nucleic acid
(d) nucleoid

Solution

(d) nucleoid

14. The cell organelle involved in forming complex sugars from simple sugars are :
(a) endoplasmic reticulum
(b) ribosomes
(c) plastids
(d) Golgi apparatus

Solution

(d) Golgi apparatus

Golgi apparatus is involved in the packaging and transport of many biomolecules such as proteins, lipids and carbohydrates.

15. Which out of the following is not a function of vacuole?
(a) Storage
(b) Providing turgidity and rigidity to the cell
(c) Waste excretion
(d) Locomotion

Solution

(d) Locomotion

Vacuoles are responsible for storage, turgidity and rigidity of the cell and waste excretion. Locomotion is carried out by specialised organelles present outside cytoplasm. Vacuoles are present inside the cytoplasm.

16. Amoeba acquires its food through a process, termed :
(a) exocytosis
(b) endocytosis
(c) plasmolysis
(d) exocytosis and endocytosis both

Solution

(b) endocytosis

The process of taking in of matter by a living cell by invagination of its membrane to form a vacuole is known as endocytosis. In endocytosis, substances that are external to a cell are brought into the cell.

17. Cell wall of which one of these is not made up of cellulose?
(a) Bacteria
(b) Hydrilla
(c) Mango tree
(d) Cactus

Solution

(a) Bacteria

Hydrilla, mango tree and cactus are plants and thus their cell wall is made up of cellulose. The cell wall of bacteria is made of polysaccharide.

18. Silver nitrate solution is used to study :
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) nucleus
(d) mitochondria

Solution

(b) Golgi apparatus

19. Organelle other than nucleus, containing DNA is :
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) mitochondria
(d) lysosome

Solution

(c) mitochondria

Mitochondria and chloroplast are the organelles that have separate DNA called as mitochondrial DNA and chloroplast DNA.

20. Kitchen of the cell is :
(a) mitochondria
(b) endoplasmic reticulum
(c) chloroplast
(d) golgi apparatus

Solution

(c) chloroplast

Food in plants is produced inside chloroplast.

21. Lipid molecules in the cell are sythesized by :
(a) smooth endoplasmic reticulum
(b) rough endoplasmic reticulum
(c) golgi apparatus
(d) plastids

Solution

(a) smooth endoplasmic reticulum

22. Cell arises from pre-existing cell was stated by :
(a) Haeckel
(b) Virchow
(c) Hooke
(d) Schleiden

Solution

(b) Virchow

23. Cell theory was given by :
(a) Schleiden and Schwann
(b) Virchow
(c) Hooke
(d) Haeckel

Solution

(a) Schleiden and Schwann

The cell theory which stated that all plants and animals are made up of cell and cell is the basic unit of life was proposed by Schleiden and Schwann.

24. The only cell organelle seen in prokaryotic cell is :
(a) mitochondria
(b) ribosomes
(c) plastids
(d) lysosomes

Solution

(b) ribosomes

25. Organelle without a cell membrane is :
(a) ribosome
(b) Golgi apparatus
(c) chloroplast
(d) nucleus

Solution

(a) ribosome

Golgi bodies, chloroplast and nucleus are all membrane bound organelles but ribosomes are organelles without membrane.

26. 1μm is :
(a) 10^–6 m

(b) 10^–9 m
(c) 10^–10 m

(d) 10^–3 m

Solution

(a) 10^–6 m

10^–3 m–millimetre

10^–6 m –Micrometer

10^–9 m –nanometer

27. Lysosome arises from :
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) nucleus
(d) mitochondria

Solution

(b) Golgi apparatus

28. Living cells were discovered by :
(a) Robert Hooke
(b) Purkinje
(c) Leeuwenhoek
(d) Robert Brown

Solution

(c) Leeuwenhoek

Robert hook observed cells first but he observed the dead cork cell. It was Leeuwenhoek who observed living cell from his microscope.

29. Select the odd one out
(a) The movement of water across a semipermeable membrane is affected by the amount of substances dissolved in it.
(b) Membranes are made of organic molecules like proteins and lipids.
(c) Molecules soluble in organic solvents can easily pass through the membrane.
(d) Plasma membranes contain chitin sugar in plants.

Solution

(d) Plasma membranes contain chitin sugar in plants.

Plant plasma membrane contains cellulose in it.

Short Answer Questions

30. Why are lysosomes known as ‘suicide-bags’ of a cell?

Solution

Lysosomes have digestive enzymes. When it bursts, the digestive enzymes are released and it starts digesting its own cells. This is the reason why lysosomes are known as suicidal bags of a cell.

31. Do you agree that “A cell is a building unit of an organism.” If yes, explain why?

Solution

Yes, the cells are the building units of an organism. Cells which perform similar functions join together to form tissues which further forms organs and organ systems.

This forms an organism. In a unicellular organism, a single cell performs all the life processes.

32. Why does the skin of your finger shrink when you wash clothes for a long time?

Solution

Soap solution is hypertonic in nature. This makes the water move out of the cells which in turn result in shrinking of fingers when you wash clothes for a long time.

33. Why is endocytosis found in animals only?

Solution

As cell wall is absent in animals, endocytosis is found only in animals. Because of this the movement of substances inside the cell is easier in animals than in plants.

34. A person takes concentrated solution of salt, after sometime, he starts vomiting. What is the phenomenon responsible for such situation? Explain.

Solution

Upon consumption of concentrated salt solution, the process of osmosis process takes place which results in dehydration. This is the reason why a person vomits.

35. Name any cell organelle which is non-membranous.

Solution

The only non-membranous cell organelle is the ribosome.

36. We eat food composed of all the nutrients like carbohydrates, proteins, fats, vitamins, minerals and water. After digestion, these are absorbed in the form of glucose, amino acids, fatty acids, glycerol, etc. What mechanisms are involved in absorption of digested food and water?

Solution

Diffusion and osmosis are involved in absorption and digestion respectively. Water is absorbed through the process of osmosis. Fatty acids and glycerol are diffused through submissive transport mechanism. Active transport helps in the absorption of glucose, amino acids and some ions.

37. If you are provided with some vegetables to cook, you generally add salt into the vegetables during cooking process. After adding salt, vegetables release water. What mechanism is responsible for this?

Solution

Vegetables release water on adding salt due to the process of osmosis. The addition of salt makes the external environment hypertonic. That is the concentration of water outside is lowered as compared to the concentration of water inside the cell. This results in the elimination of water from the vegetables due to exosmosis.

38. If cells of onion peel and RBC are separately kept in hypotonic solution, what among the following will take place? Explain the reason for your answer.
(i) Both the cells will swell.
(ii) RBCs will burst easily while cells of onion peel will resist the bursting to some extent.
(iii) (i) and (ii) both are correct.
(iv) RBC and onion peel cells will behave similarly.

Solution

The hypotonic water surrounding the cell moves inside the cell. This leads to swelling of the cells. As RBCs do not have plasma membrane, they swell and burst easily. Plant cells have cell wall which prevents them from bursting.

39. Bacteria do not have chloroplast, but some bacteria are photoautotrophic in nature and perform photosynthesis. Which part of bacterial cell performs this?

Solution

Small vesicles associated with plasma membrane are present in bacteria. These vesicles have pigment which can trap sunlight to carry photosynthesis.

40. Match the following A and B :

Solution

41. Write the name of different plant parts in which chromoplast, chloroplast and leucoplast are present.

Solution

• Chromoplast is present in flower and fruit.
• Chloroplast is found in the leaves.
• Leucoplast is present in the roots.

42. Name the organelles which show the analogy written as under :
(a) Transporting channels of the cell _____
(b) Powerhouse of the cell _____
(c) Packaging and dispatching unit of the cell _____
(d) Digestive bag of the cell _____
(e) Storage sacs of the cell _____
(f) Kitchen of the cell _____
(g) Control room of the cell _____

Solution

(a) endoplasmic reticulum
(b) mitochondria
(c) golgi body
(d) lysosome
(e) vacuole
(f) chloroplast
(g) nucleus

43. How is a bacterial cell different from an onion peel cell?

Solution

44. How do substances like carbon dioxide (CO₂) and water (H₂O) move in and out of the cell?

Solution

Carbon dioxide (CO₂) moves in and out of the cell by the process of diffusion and water (H₂O) move in and out of the cell through osmosis.

45. How does amoeba obtain its food?

Solution

Amoeba obtains its food through the process of endocytosis. Amoeba has finger-like projections which fuse with the food particles to forma food vacuole. Inside the vacuole the complex food particles are broken down into simpler ones which are then diffused into the cytoplasm.

46. Name the two organelles in a plant cell that contain their own genetic material and ribosomes.

Solution

The two organelles in a plant cell that contain their own genetic material and ribosomes are chloroplast and mitochondria.

47. Why are lysosomes also known as “scavengers of the cells”?

Solution

Lysosomes have lytic enzymes which are used to destroy the pathogens and worn-out cells. Lysosomes also destroy waste materials which are harmful for the cell. This is the reason why Lysosomes also are known as “scavengers of the cells”.

48. Which cell organelle controls most of the activities of the cell?

Solution

Most of the activities of the cell are controlled by the nucleus.

49. Which kind of plastid is more common in :
(i) Roots of the plant?
(ii) Leaves of the plant?
(iii) Flowers and fruits of the plant?

Solution

(i) Leucoplasts are more common in roots of the plant.

(ii) Chloroplasts are more common in leaves of the plant.

(iii) Chromoplasts are more common in flowers and fruits.

50. Why do plant cells possess large sized vacuole?

Solution

Vacuoles not only store important material but they also contain a sap that gives turgidity to the cell, this is the reason why plant cells possess large-sized vacuole.

51. How are chromatin, chromatid and chromosomes related to each other?

Solution

• Chromatin is a thread-like structure which forms chromosomes.
• A copy of duplicated chromosome which is generally joined to the other copy by a centromere is called Chromatid.
• When a cell starts to divide, the tangled mass of chromatin condenses into long threads and finally, rod-like bodies called chromosomes.

52. What are the consequences of the following conditions?
(i) A cell containing higher water concentration than the surrounding medium.
(ii) A cell having low water concentration than the surrounding medium.
(iii) A cell having equal water concentration to its surrounding medium.

Solution

(i) The cell loses water and shrinks if it contains higher water concentration than the surrounding medium. This is known as exosmosis.

(ii)The cell bursts if it has a lower water concentration than the surrounding medium. This process is known as endosmosis.

(iii) There is no change in the cell if a cell having equal water concentration to its surrounding medium.

Long Answer Questions

53. Draw a plant cell and label the parts which :
(a) Determines the function and development of the cell.
(b) Packages materials coming from the endoplasmic reticulum.
(c) Provides resistance to microbes to withstand hypotonic external media without bursting.
(d) Is site for many biochemical reactions necessary to sustain life.
(e) Is a fluid contained inside the nucleus.

Solution

Following is the schematic diagram of plant cell containing the specific cell organelles as asked in the question :

(a) Nucleus determines the function and development of the cell.

(b) Golgi apparatus is the package material coming from the endoplasmic reticulum.

(c) Cell wall provides the resistance to microbes to withstand hypotonic external media without bursting.

(d) Cytoplasm is a site for many biochemical reactions necessary to sustain life.

(e) Nucleoplasm is a fluid contained inside the nucleus.

54. Illustrate only a plant cell as seen under electron microscope. How is it different from animal cell?

Solution

Difference between Plant Cell and Animal Cell:

Plant Cell	Animal Cell
Cell wall present	Cell wall absent
It has a large vacuole	It has a small vacuole
Plastids are present	Plastids are absent
Centriole absent	Centriole present

55. Draw a neat labelled diagram of an animal cell.

Solution

56. Draw a well labelled diagram of a eukaryotic nucleus. How is it different from nucleoid?

Solution

Difference between Nucleus and Nucleiod:

Nucleus	Nucleiod
A membrane-bound organelle in the cytoplasm of eukaryotes.	A particular area in the cytoplasm of eukaryotes.
Contains more than one chromosome.	Contains a single chromosome.
Well-organized structure	Poorly organized structure
Spherical shaped	Irregular shaped
Nucleolus and nucleoplasm present	Nucleolus and nucleoplasm absent

57. Differentiate between rough and smooth endoplasmic reticulum. How is endoplasmic reticulum important for membrane biogenesis?

Solution

Differences between Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER):

Rough endoplasmic reticulum	Smooth endoplasmic reticulum
It possesses ribosomes attached to the membrane.	It does not possess ribosomes attached to its membrane.
Found deep inside the cytoplasm.	Found on the periphery.
Involved in protein synthesis.	Involved in lipid synthesis.
May develop from the nucleus.	May develop from the rough endoplasmic reticulum.

58. In brief state, what happens when :
(a) Dry apricots are left for sometime in pure water and later transferred to sugar solution?
(b) A Red Blood Cell is kept in concentrated saline solution?
(c) The Plasma-membrane of a cell breaks down?
(d) Rheo leaves are boiled in water first and then a drop of sugar syrup is put on it?
(e) Golgi apparatus is removed from the cell?

Solution

(a) When we put few dried raisins or apricots in plain water and leave them for some time, the cell gains water and swells. If we put the same seeds in a concentrated sugar solution, the seeds lose water, and consequently shrink.

(b) The red blood cells lose water when kept in concentrated saline solution and shrink consequently.

(c) The cell dies when the plasma membrane of a cell breaks down.

(d) The cells of rheo leaves are dead on boiling. If we put sugar solution on the dead leaves, there will be no intake of water due to lack of osmosis. Here the cell undergoes plasmolysis. This concludes that only living cells undergo osmosis.

(e) Removal of golgi apparatus stops the formation of vesicles and transport of proteins and lipids.

58. Draw a neat diagram of plant cell and label any three parts which differentiate it from animal cell.

Solution