NCERT Exemplar Solutions Class 8 Science Pollution of Air and Water

Multiple Choice Questions......................

Question 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 

Solution 1:  (b) oxygen

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. The gas is Oxygen.

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

(a) automobile exhaust

(b) burning of firewood

(c) windmill

(d) power plant 

Solution 2: (c) windmill

Since a windmill does not emit any gas into the atmosphere, it is not considered an air pollution source.

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

(a) car

(b) school bus

(c) autorickshaw

(d) scooter 

Solution 3: (b) school bus

Since school buses transport a large number of students, they emit less emissions. This will help to reduce emissions in the air.

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

(a) replace

(b) reduce

(c) reuse

(d) recycle 

Solution 4: (a) replace 

The formula for conserving natural resources is to minimise, reuse, and recycle. Replacing is not a smart way to save water.

Question 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 

Solution 5: (a) air pollution 

Air pollution from a nearby factory is making the Tajmahal's white marble yellow, causing it to deteriorate.

Question 6: Incomplete combustion of fuel such as petrol and diesel gives

(a) nitrogen oxide

(b) sulphur dioxide

(c) carbon monoxide

(d) carbon dioxide 

Solution 6: (c) carbon monoxide 

If fuels like petrol and diesel left incomplete combusted then they give us carbon monoxide.

Question 7: The phenomenon of marble cancer is due to

(a) soot particles

(b) CFCs

(c) fog

(d) acid rain 

Solution 7: (d) acid rain 

The phenomenon of marble cancer is the deterioration of buildings and monuments as a result of acid rain.

Question 8:  Potable water is the water which is

(a) obtained from a river.

(b) obtained from a lake.

(c) pure and fit for drinking.

(d) used only for washing clothes. 

Solution 8: (c) pure and fit for drinking. 

Pure and water fit for drinking is known as Potable water.

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

(a) adding chlorine tablets

(b) distillation

(c) boiling

(d) filtration 

Solution 9: (b) distillation 

By the process of distillation we will get water free from all impurities.

Question 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. 

Solution 10:  (d) swimming in the pond. 

A pond contains clean water. If any organism will swim in that pond then it will create least pollution to water rather than washing clothes, animals bathing, washing motor vehicles in the pond.

Question 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 

Solution 11:  Answer is (c) Van Mahotsav

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

(a) nitrogen gas

(b) water vapour

(c) methane gas

(d) carbon dioxide

Solution: (a) nitrogen gas

A greenhouse gas is a gas that contributes to the greenhouse effect by absorbing infrared radiation. Nitrogen is a component of atmospheric gases and has no impact on global warming.

Very Short Answer Questions.........................

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

Solution 13:  Chlorofluorocarbon is the chemical which are used and air conditioners and damage the ozone layer when released in the air.

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

Solution 14:   Two sources which cause air pollution due to suspended particulate matter are as follows:

(i) Activities related to industry

(ii) The process of burning a fuel

Question 15: Name two gases which are mainly responsible for acid rain? 

Solution 15:  Two gases which are mainly responsible for acid rain are as follows: 

(i) Nitrogen dioxide

(ii) Sulphur dioxide

Question 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? 

Solution 16:  These data can be used to raise public consciousness about air pollution.

Question 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? 

Solution 17:   Combustion of fossil fuels generates a lot of air pollution. But solar energy and wind energy can efficiently alternate fossil fuels which do not cause any pollution.

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

Solution 18:  Lead and Arsenic are two water pollutants which are toxic for plants and animals.

Short Answer Questions.........................

Question 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 off the dry leaves?

Solution 19:  Burning dry leaves is not a good idea since it pollutes the climate. Converting dry leaves to manure is the best thing to do because it does not pollute the atmosphere.

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

Solution 20:  Automobiles pause for a short time at traffic intersections, resulting in an accumulation of toxic gases at the intersection. As a result, air pollution levels are higher at a busy traffic intersection.

Question 21:  Fill in the blanks with the help of words given in bracket 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). 

(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). 

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

(d) Water which is suitable for _________ is called ________ water.

(washing, bathing, drinking, potable, soft). 

(e) Water which looks clean still has disease carrying ________ and ________ impurities.

(insects, microorganism, particles, dissolved, harmful). 

Solution 21: 

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

(b) Many industries are responsible for causing air pollution. Petroleum refineries are a major source of gaseous pollutants like sulphur-dioxide and nitrogen dioxide. 

(c) While brushing your teeth, leaving the tap running may waste several litres of water. 

(d) Water which is suitable for drinking, is called potable water. 

(e) Water which looks clean still has disease-carrying microorganisms and dissolved impurities.

Question 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.

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

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

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

(e) Water which is suitable for drinking is called soft water 

Solution 23:

a) Wrong- The write statement states that while we can live for a period of time without food, we cannot survive even for a few minutes without air.

b) True

c) Wrong - The correct statement is that carbon monoxide is created by incomplete combustion of fuels such as coal, gasoline, and diesel.

d) True

e) Wrong - Potable water is the relevant term for water that is appropriate for drinking.

Question 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.

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

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

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

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

Solution 24:

(a) Air contains 78% Nitrogen and 21% Oxygen.

(b) Vehicles produce high level of pollutants like carbon dioxide, nitrogen oxides, Carbon-monoxide and smoke.

(c) Carbon dioxide, methane, nitrous oxide and water vapour are known as greenhouse gases.

(d) Gangotri glacier in Himalaya has started melting because of global warming.

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

Long Answer Questions.........................

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

Solution 25:   Chlorofluorocarbons (CFCs) are a form of greenhouse gas. CFCs are used in appliances such as refrigerators and air conditioners. Since they deplete the ozone layers in the atmosphere, CFCs are considered pollutants. As a consequence, harmful solar radiation enters the body.

Question 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?

Solution 26:  In the Taj Mahal Zone of Agra, factories can turn to cleaner fuels such as CNG and LPG because fossil fuels release sulphur-dioxide gas into the atmosphere. This reacts with rainwater to form sulphuric acid, resulting in acid rain. Acid rain discolours the Tajmahal's white marble, turning it yellow.

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

Solution 27:  CO₂ is constantly published as a result of human activities. On the other hand, the amount of land covered by forests is shrinking. Plants use CO₂ from the atmosphere for photosynthesis, reducing CO₂ levels in the atmosphere. Since the number of trees that absorb CO₂ decreases as a result of deforestation, the amount of CO₂ in the air rises.

As a result, human actions lead to the buildup of CO₂ in the atmosphere. CO₂ is a gas that absorbs heat and prevents it from escaping into space. As a result, the earth's atmosphere's surface temperature is steadily increasing, resulting in global warming.

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

Solution 28:   We should plant trees and care for those that are already in the neighbourhood because plants absorb CO₂ and therefore help to reduce CO₂ levels in the atmosphere. This will put a stop to global warming and its consequences.

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

Solution 29:

Filtration:

This is a way of physically extracting impurities. A candle-style filter is a common household filter.

Boiling:

Boiling is a popular method for obtaining safe drinking water in many households.

Chlorination:

Chlorination is a chemical process for purifying water that is widely used. Adding chlorine tablets or bleaching powder to the water accomplishes this.

Question 30:  How can we reduce, reuse and recycle water? 

Solution 30:

Reduce:

Leaving the tap running when brushing your teeth will waste several litres of water. Every year, a tap that drips once a second loses thousands of litres of water.

Reuse:

Water used to wash vegetables can be used to water garden plants.

Recycle:

After purification, dirty water can be recycled. 

Question 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 as granted for its purity, but we must ensure the quality of water. Pollution of water originates from human activities. Through different paths, pollution reaches to groundwater. 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.

1. How do you classify the various sources of water pollution?
2. What are the point sources of water pollution?
3. Name any two non-point sources of water pollution? 

Solution 31:

1. Classification of various sources of water pollution depends upon pollution of water origination due to human activities.

(a) Point sources                                                         (b) Non-point sources

2. 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.

3. Non–point sources of pollution are those where a source of pollution cannot be easily identified. Two non-point sources of water pollution are as follows:

(a) Agricultural runoff                                                 (b) Acid rain

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

Solution 32: