NCERT Exemplar Solutions Class 8 Science Chapter 18 Pollution of Air and Water

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NCERT Exemplar Solutions Class 8 Science Solutions Chapter 18 Pollution of Air and Water

1. Air is a mixture of various gases. One of the gases is 21% part of the air and is essential for the survival of human beings. This gas is

(a) Nitrogen

(b) Oxygen

(c) Ozone

(d) Argon

Ans: (b) Air is a blend of gases, with one gas constituting 21% of the mixture and being vital for human survival. This gas is oxygen, making up 21% of the atmosphere, while nitrogen accounts for 78.09%, argon for 0.93%, and other gases for 0.3%.

2. Which of the following is not a source of air pollution?

(a) Automobile exhaust

(b) Burning of firewood

(c) Windmill

(d) Power plant

Ans: (c) Which of the following is not a source of air pollution? The answer is (c) Windmills, as they do not emit harmful gases, thus not contributing to air pollution.

3. Boojho wishes to contribute to reducing air pollution. Which vehicle should he use for going to school?

(a) Car

(b) School bus

(c) Auto-rickshaw

(d) Scooter

Ans: (b) To reduce air pollution, Boojho should use the school bus for commuting to school. Opting for the school bus helps reduce traffic congestion as it is a public mode of transportation.

4. Which of the following is not a way to conserve water?

(a) Replace

(b) Reduce

(c) Reuse

(d) Recycle

Ans: (a) The most effective ways to conserve water are to reduce, reuse, and recycle (the 3R formula). Replacing water is not a sustainable solution for water conservation.

5. The type of pollution which is likely to affect Taj Mahal in Agra to a greater extent is

(a) Air pollution

(b) Water pollution

(c) Soil pollution

(d) Noise pollution

Ans: (a) The pollution type that significantly impacts the Taj Mahal in Agra is air pollution, posing a threat to this iconic monument.

6. Incomplete combustion of fuel such as petrol and diesel gives

(a) Nitrogen oxide

(b) Sulphur dioxide

(c) carbon monoxide

(d) carbon dioxide

Ans: (c) Incomplete combustion of fuels like petrol and diesel produces carbon monoxide, a highly toxic gas.

7. The phenomenon of marble cancer is due to

(a) Soot Particles

(b) CFCs

(c) Fog

(d) Acid Rain

Ans: (d) Marble cancer, a phenomenon, is caused by acid rain resulting from the reaction of SO2 and NO2 gases with water, forming acids like sulphuric and nitric acid.

8. Potable water is the water that is

(a) Obtained from a river.

(b) Obtained from a lake.

(c) Pure and fit for drinking.

(d) Used only for washing clothes.

Ans: (c) Potable water is pure and suitable for drinking, not obtained from rivers or lakes, solely used for washing clothes.

9. Which of the following procedures will give you water free from all impurities?

(a) Adding chlorine tablets

(b) Distillation

(c) Boiling

(d) Filtration

Ans: (b) Distillation is a process that removes all impurities from water, providing water free from contaminants.

10. A pond contains clean water. Which of the following activities will produce the least pollution of water?

(a) Washing clothes in the pond

(b) Animals bathing in the pond

(c) Washing motor vehicles in the pond

(d) Swimming in the pond.

Ans: (d) Swimming in a pond causes the least pollution compared to washing clothes, bathing animals, or washing vehicles, as it does not introduce harmful chemicals into the water.

11. Trees help in reducing the pollution of our environment. Lakhs of trees are planted by people in the month of July every year. The occasion is called

(a) Forest Conservation Day

(b) Plantation month

(c) Van Mahotsav

(d) Wildlife week

Ans: (c) “Van Mahotsav” is celebrated in July every year, where people plant numerous trees to help reduce environmental pollution.

12. Which of the following is not a greenhouse gas?

(a) Nitrogen gas

(c) Methane gas

(b) Water vapour

(d) Carbon dioxide

Ans: (a) Nitrogen gas is not a greenhouse gas, unlike methane, water vapor, and carbon dioxide, as it does not contribute to global warming.

Very Short Answer Questions

13. Name the chemicals which are used in refrigerators and air conditioners and damage the ozone layer when released into the air.

Ans: Chlorofluorocarbons are chemicals used in refrigerators and air conditioners that harm the ozone layer when released into the air.

14. Name any two sources which cause air pollution due to suspended particulate matter.

Ans: Sources of air pollution due to suspended particulate matter include industrial activities and fuel combustion by automobiles.

15. Name two gases that are mainly responsible for acid rain?

Ans: Sulphur dioxide (SO2) and nitrogen dioxide (NO2) are the primary gases responsible for causing acid rain.

16. The quality of air at various locations is monitored regularly by the government and other agencies? In what way can you use these data?

Ans: Air quality data monitored by the government can be utilized to raise awareness about air pollution and its impact on our surroundings.

17. Combustion of fossil fuels generates a lot of air pollution. Can you suggest any two alternative sources of energy which do not cause any pollution?

Ans: Solar energy and wind energy are two pollution-free alternative sources of energy to combat the pollution caused by the combustion of fossil fuels.

18. Name any two water pollutants which are toxic for plants and animals.

Ans: Arsenic and lead are toxic water pollutants harmful to plants and animals, causing deformities in their bodies.

Short Answer Questions

19. A lot of dry leaves are collected in a school garden and are burnt every day. Do you think that it is right to do so? If not, what should be done to dispose of the dry leaves?

Ans: Burning dry leaves in a school garden leads to air pollution; composting them is a sustainable alternative to obtain manure.

20. The level of air pollution is higher at a busy traffic intersection. Why?

Ans: Busy traffic intersections have higher air pollution levels due to the accumulation of vehicles emitting toxic gases, leading to elevated levels of suspended particulate matter in the air.

21. Fill in the blanks with the help of words given in brackets after each sentence.

(a) When air is contaminated by ________ substances which have a ________ effect on both the ________ and ________, it is referred to as ________. (Air pollution, harmful, living, unwanted, non-living, pollutants).

Ans: Unwanted, harmful, living, non-living, air pollution.

(b) Many ________ are responsible for causing ________ pollution. Petroleum ________ are a major source of ________ pollutants like ________ and ________. (Sulphur dioxide, refineries, industries, nitrogen dioxide, gaseous, liquid, people, air).

Ans: Industries, air, refineries, gaseous, sulphur dioxide, nitrogen dioxide.

(c) While ________ your teeth, leaving the ________ running may waste several ________ of water. (Tap, litres, brushing, washing, drops)

Ans: Brushing, tap, litres.

(d) Water which is suitable for _________ is called ________ water. (Washing, bathing, drinking, potable, soft).

Ans: Drinking, potable

(e) Water which looks clean still has disease carrying ________ and ________ impurities. (Insects, microorganisms, particles, dissolved, harmful).

Ans: Microorganisms, dissolved.

22. Match the following:

Column I	Column II
Sulphur oxide	i) Damage ozone layer
Carbon dioxide	ii) Reduce oxygen-carrying capacity of the blood
Carbon monoxide	iii) Acid rain
Chlorofluorocarbons	iv) Greenhouse gas

Ans: The answers to Column I are written in front of Column II.

Column I	Column II
Sulphur oxide	iii) Acid rain
Carbon dioxide	iv) Greenhouse gas
Carbon monoxide	ii) Reduce the oxygen-carrying capacity of the blood.
Chlorofluorocarbons	i) Damage the ozone layer.

23. Find out the wrong statements and write them in their correct form.

(a) We can survive for some time without air but we cannot survive even for a few minutes without food.

Ans: We can survive for some time without food, but we cannot survive even for a few minutes without air.

(b) A brick kiln emits a lot of smoke and other harmful gases causing air pollution.

Ans: Correct statement.

(c) Carbon monoxide is produced by the complete burning of fuels such as coal, petrol, and diesel.

Ans: Carbon monoxide is produced by incomplete burning of fuels such as coal, petrol, and diesel.

(d) Chlorination is a commonly used chemical method for killing germs in the water.

Ans: Correct statement.

(e) Water that is suitable for drinking is called soft water.

Ans: Water that is suitable for drinking is called potable water.

24. In the following statements, the underlined words are jumbled up. Write them in their correct form.

(a) Air contains 78% ginroten and 21% gonexy.

Ans: Air contains 78% Nitrogen and 21% Oxygen.

(b) Vehicles produce high levels of pollutants like carbon dioxide, nitrogen oxides, nobrac moondexi and mosek.

Ans: Vehicles produce high levels of pollutants like carbon dioxide, nitrogen oxides, carbon-monoxide, and smoke.

(c) Carbon dioxide, thaneme, nitrous oxide and water vapour are known as heengrouse sesga.

Ans: Carbon dioxide, methane, nitrous oxide, and water vapor are known as greenhouse gases.

(d) Gangotri glacier in Himalaya has started melting because of lablog ringwam.

Ans: Gangotri glacier in Himalaya has started melting because of global warming.

(e) Whenever harmful substances such as wagese, toxic chemicals, silt, etc. get mixed with water, the water becomes potdulle.

Ans: Whenever harmful substances such as sewage, toxic chemicals, silt, etc. get mixed with water, the water becomes polluted.

Long Answer Questions

25. What do CFCs stand for? Name some devices where CFCs are used. Why are CFCs considered pollutants?

Ans: CFCs stand for Chlorofluorocarbons. These gases are used in air conditioners and refrigerators. CFCs are considered pollutants that contribute to the depletion of the ozone layer.

26. Why is it advised that industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra?

Ans: Industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra to reduce air pollution and prevent acid rain, which deteriorates the monument’s condition.

27. It is said, “CO2 contributes to global warming.” Explain.

Ans: CO2 contributes to global warming by trapping heat in the Earth’s atmosphere, increasing the planet’s temperature, and leading to various climate changes.

28. We should plant trees and nurture the ones already present in the neighbourhood. Why?

Ans: Planting trees and nurturing existing ones help decrease the levels of carbon dioxide in the environment and increase the levels of oxygen, mitigating global warming.

29. Explain the traditional way of purifying water to make it fit for drinking.

Ans: Traditional water purification methods include filtration, boiling, and chlorination. Filtration involves using filters or filter rods, boiling raises the temperature to kill germs, and chlorination adds chlorine to water in the form of tablets or bleaching powder.

30. How can we reduce, reuse and recycle water?

Ans: Water can be reduced by closing the tap while brushing, changing leaky taps, and using a bucket during baths. Water can be reused by filtering RO water for cleaning floors and using water from washing fruits and vegetables to water plants. Water can be recycled by purifying dirty water through filtration.

31. Read the paragraph and answer the questions following it. Water is essential for life. Without water, there would be no life. We usually take water for granted for its purity, but we must ensure the quality of water. Pollution of water originates from human activities. Through different paths, pollution reaches groundwater. An easily identified source or place of pollution is called a point source, e.g. municipal and industrial discharge pipes, where pollutants enter the water source. Non–point sources of pollution are those where a source of pollution cannot be easily identified, e.g. agricultural runoff, acid rain etc.

(i) How do you classify the various sources of water pollution?

Ans: Water pollution sources are classified as point sources, which are easily identifiable, and non-point sources, which are not easily identifiable.

(ii) What are the point sources of water pollution?

Ans: Point sources of water pollution include municipal and industrial discharge pipes.

(iii) Name any two non-point sources of water pollution?

Ans: Agricultural runoff and acid rain are examples of non-point sources of water pollution.

32. Complete the crossword puzzle with the help of clues given below:

Across

1. Pollutant which was used in refrigerators and air conditioners. (18)
2. Produced on incomplete combustion of fuels. (14)
3. This chemical protects our crops and is washed into water bodies from the field. (9)

Down

2. This layer protects us from harmful ultraviolet rays. (5)
3. It is essential for combustion. (6)
4. Disease which is caused by drinking contaminated water. (7)
5. River which is famous in India and sustains most of the northern, central and eastern Indian population. (5)

Ans:

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