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Pollution Of Air And Water

Class 8th Science NCERT Exemplar Solution
Multiple Choice Questions
  1. Air is a mixture of various gases. One of the gases is 21% part of the air and is…
  2. Which of the following is not a source of air pollution?
  3. Boojho wishes to contribute in reducing air pollution. Which vehicle should he use for…
  4. Which of the following is not a way to conserve water?
  5. The type of pollution which is likely to affect Taj Mahal in Agra to a greater extent is…
  6. Incomplete combustion of fuel such as petrol and diesel gives:
  7. The phenomenon of marble cancer is due to
  8. Potable water is the water which is
  9. Which of the following procedures will give you water free from all impurities?…
  10. A pond contains clean water. Which of the following activities will produce least…
  11. Trees help in reducing the pollution of our environment. Lakhs of trees are planted by…
  12. Which of the following is not a green house gas?
Very Short Answer Type
  1. Name the chemicals which are used in refrigerators and air conditioners and damage ozone…
  2. Name any two sources which causes air pollution due to Suspended Particulate Matter…
  3. Name two gases which are mainly responsible for acid rain.
  4. The quality of air at various locations is monitored regularly by government and other…
  5. Combustion of fossil fuels generates a lot of air pollution. Can you suggest any two…
  6. Name any two water pollutants which are toxic for both plants and animals.…
Short Answer Type
  1. A lot of dry leaves are collected in a school garden and burnt every day. Do you think…
  2. The level of air pollution is higher at a busy traffic intersection. Why?…
  3. Fill in the blanks with the help of words given in the bracket after each sentence.(1)…
  4. Match the items of Column A with those of Column B. Table
  5. Find out the wrong statements and write them in their correct form.(1) We can survive for…
  6. In the following statements the underlined words are jumbled up. Write them in their…
Long Answer Type
  1. What do CFCs stand for? Name some devices where CFCs are used. Why CFCs are considered as…
  2. Why is it advised that industries should switch over to cleaner fuels such as CNG and LPG…
  3. It is said, "CO2 contributes to global warming". Explain?
  4. We should plant trees and nurture the ones already present in the neighborhood. Why?…
  5. Explain traditional ways of purifying water to make it fit for drinking.…
  6. How do we reuse, reduce and recycle water?
  7. Read the paragraph and answer the questions following it.Water is essential for life.…
  8. Complete the crossword puzzle with the help of clues given below:…

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


Answer:

Oxygen is the gas that is necessary for the survival of human beings. The gases in Earth's atmosphere are:

Nitrogen — 78 percent.


Oxygen — 21 percent.


Argon — 0.93 percent.


Carbon dioxide — 0.04 percent.


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


Answer:

Windmills are not a source of air pollution.

Air pollution happens when harmful gases and particles are released into the air.


Windmill helps convert wind into energy that can then be used for various purposes. A windmill serves as an alternative source of energy that is clean too.


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. auto rickshaw

D. scooter


Answer:

Boojho should use a school bus if he wants to help reduce air pollution.

By using the school bus, the number of vehicles being used will reduce. Instead of 20 cars or 20 scooters one bus would carry 20 children.


20 cars or scooters would have caused a lot of pollution which got reduced because of one school bus being used.


Question 4.

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

B. reduce

C. reuse

D. recycle


Answer:

Replacing is not a way of conserving water.

Conserving water means saving water so that we don’t run out of it in future. Water conservation policies involve ways in which e can meet the current and future human demand of water.


By replacing water we won’t be able to save water in anyway. We can conserve water by reducing the use, for example, closing the tap when brushing teeth or using bucket instead of shower.


We can conserve water by reusing. For example, water from the RO water purifiers can be collected and reused for washing the floor.


We can also recycle water. For example, water harvesting. Water from the rain can be collected and used for various purposes.


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


Answer:

The Taj Mahal is made from white marble which gets affected by the pollutants such as dust and soot from the industries and factories around it. All this is turning the white marble surface of Taj Mahal yellow.


Question 6.

Incomplete combustion of fuel such as petrol and diesel gives:
A. nitrogen oxide

B. sulphur dioxide

C. carbon monoxide

D. carbon dioxide


Answer:

Carbon Monoxide is produced as a result of incomplete combustion of fuels.

Incomplete combustion happens when there’s not enough oxygen present or there’s poor supply of air. As a result of this, instead of CO2, CO (Carbon monoxide) is produced.


Carbon monoxide is a harmful and poisonous gas.


Question 7.

The phenomenon of marble cancer is due to
A. Soot particles

B. CFCs

C. Fog

D. acid rain


Answer:

Marble cancer refers to the phenomenon of corrosion of marble due to the action of SO2 and NO2.

Acid rain happens because of SO2 and NO2 that are released into the air.The SO2 and NO2 react with water, oxygen and other chemicals to form sulfuric and nitric acids.


Sulfuric acid and nitric acid in the rain dissolve marble to form salts.


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


Answer:

Potable water reefers to water that is fit for human consumption. Water can be made potable by various methods.

Potable water is also known as drinking water.


One way of making water potable is by boiling it.


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


Answer:

Distillation of water will make the water pure from all impurities.

In distillation, water first gets boiled into vapor and it is then condensed back into liquid in a separate container.


Impurities in the original water that do not boil below or near the boiling point of water remain in the original container.



Question 10.

A pond contains clean water. Which of the following activities will produce 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


Answer:

Swimming in the pond will produce the least pollution of water because no harmful pollutants or any chemicals would be involved in the process.

•Washing of clothes would release the soap and detergent being used in to the water.


•Animals might be covered with dust and excreta which when they bathe will get washed in the water of the pond.


•Washing motor vehicles too would cause pollution because motor vehicles produce soot and other harmful particles which will get washed in the water.


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


Answer:

Van Mohatsav is celebrated every July for One week. During Van Mohatsav, millions of saplings are planted across India.

Forest Conservation Day is celebrated on 21st March.


The first week of October is celebrated as Wildlife Week in India.


Question 12.

Which of the following is not a green house gas?
A. nitrogen gas

B. water vapour

C. methane gas

D. carbon dioxide


Answer:

Nitogen gas is not a green house gas.

Green houses gases are the gases in Earth's atmosphere that trap heat.


The main greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone.



Very Short Answer Type
Question 1.

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


Answer:

The chemicals used in refrigerators and air conditioners, which damage the ozone layer when released in the air, are called CFCs or Chlorofluorocarbons.


CFCs are made up of chlorine, fluorine and carbon elements. When ultraviolet light waves (UV) strike CFC molecules in the atmosphere, the carbon-chlorine bond breaks and a chlorine atom is produced. The chlorine atom then reacts with an ozone (O3) molecule and breaks and damages the ozone layer.



Question 2.

Name any two sources which causes air pollution due to Suspended Particulate Matter


Answer:

Suspended particulate matter or SPM are fine solids or liquids particles that may be dispersed through the air because of activities like combustion processes, industrial activities or natural sources (like volcanic eruptions.)


Two sources which may cause air pollution due to SPM are:


a) Automobiles: Automobiles run on petrol and diesel burning of which produces SPM which get suspended in the air.


b) Industrial activities: Activities like mining, construction, building demolition also release SPM in the air. These activities release a large amount of dust particles in the air which get picked up by the wind and get suspended in the air around.



Question 3.

Name two gases which are mainly responsible for acid rain.


Answer:

The two main gases responsible for acid rains are SO2 and NO2 i.e. Sulphur dioxide and Nitrogen dioxide.


These gases react with water, oxygen and other chemicals and form Sulphuric acid and nitric acid.


These acids then combine with water and fall down in the form of acid rain.



Question 4.

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


Answer:

The air quality is monitored by the government and various other agencies. These data can be used to create awareness about the air quality among people.

People can be informed about what levels are acceptable and what levels are not.


These data can be further used to teach people about the Air quality index and what the numbers mean. Public health risks increase as the AQI rises.



Question 5.

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?


Answer:

Fossil fuels generate a lot of air pollution when they undergo combustion. Instead of these, we can use alternative sources of energy like:


1) Solar energy: Solar panels can be installed which would harness or use the solar energy of the sun to run machines or generate power.


2) Wind energy: In wind energy, wind is used as a source of energy. Wind turbines are installed which generate energy when turned.



Question 6.

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


Answer:

Lead and arsenic are two water pollutants that are harmful for both plants and animals alike.


Lead causes morphological dysfunctions in plants and poisons animals as it accumulates in the body.


Arsenic accumulates in plant and animal bodies and leads to deformities and death.




Short Answer Type
Question 1.

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


Answer:

No, burning of the leaves is not the right thing to do. Burning causes air pollution. Burning of leaves leads to smoke formation that contains harmful gases like Carbon monoxide and even particulate matter.

To dispose dry leaves, one can compost them. Composting is good for the soil and doesn’t cause any pollution.



Question 2.

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


Answer:

The level of air pollution is higher at a busy traffic intersection because a large number of cars, buses and other automobiles stop there at multiple times throughout the day. Their automobiles release a large amount of gases that contain the various pollution causing gases. The SPM given out by them gets suspended in the air around that area making it polluted.



Question 3.

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

(1) When air is contaminated by ________ substances which have a ________ effect on both the ________ and _______, it is referred to as ________.

(2) 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 ).

(3) While ________ your teeth, leaving the ______ running may waste several ______ of water.

(tap, litres, brushing, washing, drops ).

(4) Water which is suitable for _______ is called _______ water.

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

(5) Water which looks clean still has disease carrying _______ and _______ impurities.

(insects, micro organism, particles, dissolved, harmful).


Answer:

1. unwanted, harmful, living, non-living, air pollution.

2. industries, air, refineries, gaseous, sulphur dioxide, nitrogen dioxide.


3. brushing, tap, litres


4. drinking, potable


5. microorganisms, dissolved.



Question 4.

Match the items of Column A with those of Column B. Table



Answer:

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


a) Sulphur dioxide (SO2) is one of the gases that are responsible for causing acid rain. The other gas is Nitrogen dioxide.


b) Carbon dioxide is one the 5 main greenhouse gases. The other three are: water vapor, methane, nitrous oxide and ozone.


c) Carbon monoxide reduced oxygen carrying capacity of the blood. Oxygen has hemoglobin which carries oxygen. Hemoglobin however, has a higher affinity for Carbon monoxide which means carbon monoxide can bind to hemoglobin more easily than oxygen. So when carbon monoxide is present, hemoglobin binds to it rather than to oxygen and reduces the amount of oxygen being carried by the blood.


d) CFCs or chlorofluorocarbons damage the ozone layer. CFCs are broken down by the UV radiations and release chlorine atoms. These chlorine atoms destroy the ozone.



Question 5.

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

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

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

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

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

(5) Water which is suitable for drinking is called soft water.


Answer:

Statements (b) and (d) are correct statements.


The correct form of statements (a), (c) and (e) are as follows:


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


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


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



Question 6.

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

(1) Air contains 78% ginroten and 21% goncxy.

(2) Vehicle produce high level of pollutants like carbon dioxide, nitrogen oxide, nobrac moondexi and mosek.

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

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

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


Answer:

1) Air contains 78% nitrogen and 21% oxygen.


2) Vehicles produce high levels of pollutants like carbon dioxide, nitrogen oxide, carbon monoxide and smoke.


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


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


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




Long Answer Type
Question 1.

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


Answer:

CFCs stand for Chlorofluorocarbons. Chlorofluorocarbons are used in refrigerators, air conditioners and aerosol sprays.

CFCs are known as pollutants because CFCs damage the ozone layer of the atmosphere.


CFCs are broken down by the ultraviolet radiations and chlorine is produced. Chlorine then goes ahead and destroys the ozone layer.



Question 2.

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


Answer:

It is advised that industries around the Taj Mahal should switch over to cleaner fuels such as CNG and LPG because pollutants in air are discolouring white marble of Taj Mahal.


This discolouration is known as marble cancer. The sulphur dioxide and nitrogen dioxide gases being released by industries are causing acid rains. Acid rain dissolves the marble of the Taj Mahal.


Taj Mahal is one the Seven Wonders of the World and generates a lot of tourism. If the beauty of Taj Mahal fades, it would be a cause for concern on a national scale.


CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas) are ecofriendly and cause no harm to the environment. Therefore, it is advised that industries should switch over to CNG and LPG.



Question 3.

It is said, "CO2 contributes to global warming". Explain?


Answer:

Carbon dioxide (CO2) is a greenhouse gas. This means that carbon dioxide is able to trap the heat and prevents it from escaping the Earth’s atmosphere.

When the amount of carbon dioxide in the atmosphere increases, the amount of heat trapped also increases. This makes the average temperature of the Earth rise up making it hotter.


This above average warming up of the Earth’s atmosphere is known as global warming.



Question 4.

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


Answer:

We need to plant trees and nurture the ones already present because trees are an important source of controlling global warming.

Plants use carbon dioxide from the atmosphere for their own activity and give out oxygen in exchange. They reduce the excess amount of carbon dioxide by utilizing it, thus helping in prevention of global warming.


Plants further, hold up the soil together and prevent erosion.


Plants also help in maintain the groundwater level.


They further help in purifying the air and reducing air pollution.



Question 5.

Explain traditional ways of purifying water to make it fit for drinking.


Answer:

There are different ways of purifying water like:

•Boiling


•Filtration


•Distillation


•Addition of Chlorine tablets


Boiling: Boiling water is the safest method of purification. Boiling is enough to kill pathogenic bacteria and other harmful microorganisms.


Filtration: In this method, water is purified by passing it through a filter which is some kind of a membrane. Filtration collects the suspended impurities in water and purifies it.


Distillation: In distillation, water first gets boiled into vapor and it is then condensed back into liquid in a separate container, thus making it pure.


Chlorination: Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets or bleaching powder to the water.



Question 6.

How do we reuse, reduce and recycle water?


Answer:

The 3 Rs of conservation are: Reuse, reduce and recycle.

These three Rs can be applied to water conservation as well.


Reusing: Water can be reused. For example, water from RO water purifiers can be used to wash the floor. Further, water that we use to wash grains and vegetables can be used to water the plants in the garden.


Reducing: A lot of water gets wasted while performing everyday tasks like bathing and brushing. While brushing teeth we can turn off the tap when the water is not required. Also, showering wastes a lot of water so using bucket to take a bath is advisable. Also, rain water can be harvested or saved to be reused for various purposes.


Recycle: Water can be purified by various methods and recycled.



Question 7.

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 ground water. Easily identified source or place of pollution is called as 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?

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

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


Answer:

i) The various sources of water pollution are classified as point sources and non-point sources.


ii) A point source of pollution is a single, identifiable source of water pollution. Examples of point sources include sewage treatment plants.


iii) Non point source pollution results from multiple sources. Examples of non-point sources of pollution are acid rains and agricultural run-off water.



Question 8.

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





Answer:

1. CFCs or Chlorofluorocarbons were used in refrigerators and air conditioners earlier.


2. The ozone layer found in the Stratosphere protects us from harmful UV radiations.


3. Carbon monoxide is produced when incomplete combustion of fuel takes place.


4. Oxygen is required for combustion to take place.


5. Cholera is caused by drinking impure or contaminated water.


6. Pesticides are chemicals that help protect crops from the harmful actions of pests. However, these are harmful and poisonous substances, which when crops are watered, get washed away with it causing water pollution.


7. The Ganga river is famous in India and sustains most of the northern, central and eastern Indian population.