NCERT SOLUTIONS FOR CLASS 8 SCIENCE POLLUTION OF AIR AND WATER CHAPTER 18

Question 1.
What are the different ways in which water gets contaminated?

Following are the ways by which water gets contaminated:

  • People dispose of garbage in the water.
  • Many industries discharge their harmful chemicals directly into rivers and streams.
  • Chemical fertilisers, pesticides and weedicides used in agricultural practices get dissolve in water and are washed away into water bodies from the fields.
  • Untreated sewage is directly discharged into water from household activities.

Question 2.
At an individual level, how can you help to reduce air pollution?

I can do the following things to reduce air pollution:

  • I will use public transport as far as possible.
  • I will generate awareness among people to reduce air pollution.
  • I will plant more and more trees because trees help to keep the environment clean and reduce air 1 pollution.
  • I will not use vehicles for short distances.

Question 3.
Clear, transparent water is always fit for drinking. Comment.

No, this is not true that clean, transparent water is always fit for drinking. It is possible that they may carry disease-causing microorganisms. Thus, it is good to purify water before drinking..

Question 4.
You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.

These are the measures that would help our town to ensure the supply of clean water to all its residents:

  • Chlorine tablets should be made available.
  • Proper cleaning of the water tank from time to time.
  • The water supply pipes should not come in contact with the sewage pipes.

Question 5.
Explain the differences between pure air and polluted air.

Pure air contains 78% nitrogen, 21% oxygen and 0.03% C02. Other gases such as argon, methane, neon, water vapour, etc. are also found in small quantities. When this air is contaminated by unwanted substances which have harmful effect on both living and non-living things like nitrogen oxide, sulphur oxide, carbon monoxide, etc., is said to be polluted.

Question 6.
Explain circumstances leading to acid rain. How does acid rain affect us?

Nitrogen dioxide, sulphur dioxides are the pollutants which react with the water vapour present in atmosphere to form sulphuric acid and nitric acid. These acids come down with the rain, making the rain acidic. This is called acid rain.
Following are the affects of acid rain:

  • It increases corrosion of metals.
  • It damages buildings and sculptural materials.
  • It removes the basic nutrients such as calcium from the soil.
  • It causes direct damage to plants and crops.
  • It causes skin eruptions in human being.

Question 7.
Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen

(d) Nitrogen

Question 8.
Describe the ‘Greenhouse Effect’ in your own words.

Basically, the greenhouse effect means the warming of the earth’s environment. When the sun’s ray falls on the earth, a part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. Greenhouse gases present in the atmosphere trap these radiations and do not allow heat to leave. This helps in keeping our planet warm and thus helps in survival. CO2, methane and CO are the gases responsible for this effect.

Question 9.
Prepare a brief speech on global warming. You have to deliver the speech in your class.

Good Morning,
Respected teacher and my dear friends,
As we all know the continuous increase in the temperature of the earth is called global warming. Global warming is basically caused by pollution of air, excessive heat which is trapped by greenhouse gases. Global warming is a threat to life as it causes a lot of health problems. We may have to face dire consequences due to global warming.
That’s all friends. Thank you for the attention. Have a good day.

Question 10.
Describe the threat to the beauty of the Taj Mahal.

Taj Mahal has become a matter of concern due to pollutants in air that are discolouring its white marble. Acid rains due to increasing air pollution has started corroding the marble. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards the yellowing of the marble. Thus making Taj Mahal losing its beauty.

Question 11.
Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Increased level of nutrients in the water affect the survival of aquatic organisms as these act as nutrients for algae to flourish and once these algae die, they serve as food for decomposers like bacteria and a huge amount of oxygen in water body gets used up. This results in decrease in the oxygen level, which may kill aquatic organisms.

Question 12.
Write two causes of soil pollution.

Two causes of soil pollution are excessive use of chemical fertilizers and disposal of waste materials.

Question 13.
What is the full form of CFC ?

CFC — Chlorofluorocarbons

Question 14.
Which of the following is not a greenhouse gas? [NCERT]
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen

(b) Sulphur dioxide and
(d) nitrogen.

Question 15.
What is meant by air pollution ?

The presence of unwanted substances in the air which have a harmful effect on living and non-living components is known as air pollution.

Question 16.
What name is given to unwanted substances present in the air ?

Air pollutants.

Question 17.
Name the pollutants which are added from natural sources.

Smoke and dust from forest fires or volcanic eruptions.

Question 18.
Name the pollutants added by vehicles.

Carbon monoxide, carbon dioxide, nitrogen oxides and smoke.

Question 19.
What are the harmful effects of smog ?

Smog Causes breathing diseases such as asthma, cough and wheezing in children. ‘

Question 21.
Which gases are released from petroleum refineries ?

Sulphur dioxide and nitrogen dioxide.

Question 23.
How are CFCs added in the atmosphere ?

CFCs are released from aersol sprays, refrigerators and air conditioners.

Question 24.
What harm is caused by the presence of CFCs ?

CFCs destroy the ozone layer which protects us from harmful ultraviolet rays of the sun.

Question 25.
Name one important monument which has been affected by air pollution ?

Taj Mahal located at Agra.

Question 26.
Expand SPM.

Suspended Particulate Matter.

Question 27.
Name some greenhouse gases.

Carbon dioxide, methane, nitrous oxide and water vapour.

Question 28.
What is meant by polluted water.

Whenever substances such as sewage, toxic chemicals, silt, etc., which are harmful to life, get mixed with water, the water is said to be polluted.

Question 29.
What is potable water ?

Water which is suitable for drinking is called potable water.

Question 30.
How can pollution by industries checked ?

The industrial waste should be treated before discharging into the rivers.

Question 31.
What is rain mixed with sulphuric acid called ?

Acid rain.

Question 32.
Name two smokeless fuels.

LPG and CNG.

Question 33.
Which compound is added to petrol to prevent engines from ‘knocking’ ?

A lead compound is added to petrol to prevent engines from knocking.

Question 34.
Name one biodegradable fertiliser.

Compost.

Question 35.
What is meant by water table ?

Diarrhoea, dysentry and jaundice.

Question 36.
What should be our main strategy to deal with the environmental problems faced by us?

To develop technology that uses :

  • Renewable sources of energy like solar energy, wind energy, etc. and avail maximum benefit from them.
  • Less amount of non-renewable sources of energy, so that they last longer.

Question 37.
Mention two human activities which affect the quality of the soil on a large scale.

Question 37.
What are the two ways to conserve soil?

  • By planting more trees and grass.
  • By constructing dams and river embankments.

Question 38.
Explain the differences between pure air and polluted air ? 

Pure air means air which does not have any undesirable gases and particles in it. It does not’ affect living or non-living things. But polluted air contains harmful pollutants which affect living and non-living things.

Question 39.
Clear, transparent water is always fit for drinking. Comment. 

This statement is not correct because clear and transparent water may contain harmful bacteria which cannot be seen. They can cause diseases in human beings.

Question 40.
Why are many people suffering from respiratory problems these days ?

Many people are suffering from respiratory problems due to air pollution.

Question 41.
The number of vehicles are increasing rapidly. How is this causing air pollution ?

The vehicles produce high levels of carbon monoxide, carbon dioxide, nitrogen oxides and smoke, which contribute to air pollution.

Question 42.
How is carbon monoxide produced the vehicles ?

Carbon monoxide is produced by incomplete combustion of fuels such as petrol and diesel.

Question 43.
How is smog produced ?

Oxides of nitrogen combine with other pollutants and fog contributing to the formation of smog.

Question 44.
How is sulphur dioxide produced in the atmosphere ?

Sulplur dioxide is produced by combustion of fuels like coal in power plants.

Question 45.
How is suspended particulate matter harmful ?

Suspended particulate matter reduces visibility and if inhaled causes respiratory diseases.

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