NCERT Solutions for Class 8 Science, Chapter 18 - Pollution of Air and Water

The NCERT Class 8 Science, Chapter 18 deals with the problem of pollution of air and water and the pollutants that causes pollution. The agents that pollute our environment are called pollutants. They contaminate air, water and land. The chapter begins with air pollution (the contamination of air by impurities which may have a harmful impact on the living and non- living components) and its sources, then you will study the steps to prevent air pollution, the greenhouse effect and global warming. As you move further in this chapter you will study water pollution, its causes, what is potable water and how is water purified.

To know more about NCERT Solutions for Class 8, Science Chapter 18 – Pollution Of Air and Water, let’s look at the topics and sub-topics of this chapter :

18.1 Air Pollution

18.2 How does Air Get Polluted?

18.3 Case Study – The Taj Mahal

18.4 Greenhouse Effect

18.5 What can be done?

18.6 Water Pollution

18.7 How does water get polluted?

18.8 What is potable water and how is water purified?

18.9 What can be done?

In Class 8 Science Chapter 18, you will learn-

Section 18.1 – In this section, you will study air pollution. The section begins with the introduction to pollution followed by air pollution. An undesirable change in the physical, chemical or biological characteristics of air, water and land that may be harmful to human life and other animals, living conditions, industrial processes and cultural assets. Air pollution is the contamination of air by impurities which may have a harmful impact on the living organisms and the non-living components.

Section 18.2 – This section will teach you the causes of air pollution. The substances which contaminate the air are called air pollutants. They pollute our environment. For example – smoke, dust, fog and gases like sulphur dioxide and nitrogen dioxide. The sources of air pollution can be natural or man-made. Smoke and dust arising from forest fires or volcanic eruptions, methane gas arising from decaying organic matter are the natural sources whereas exhaust gases from factories, power plants and automobiles are the man-made resources. Carbon monoxide, nitrogen oxides, carbon dioxide, methane and sulphur dioxide are the major pollutants of air.

Section 18.3 – This section deals with a case study on air pollution – The Taj Mahal. Over the past two decades, Taj Mahal located in Agra has become a matter of concern. Pollutants in the air are discolouring its white marble. So, it is not only living organisms that get affected by polluted air but non-living things like buildings, monuments and statues also get affected. The industries located in and around Agra like rubber processing, automobile, chemical, and especially the Mathura oil refinery, have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide. Acid rain corrodes the marble of the monument causing ‘Marble cancer’. The Supreme Court has ordered industries to switch to cleaner fuels like CNG and LPG. Moreover, the automobiles should switch over to unleaded petrol in the Taj zone.

Section 18.4 – This section deals will brief you about the greenhouse effect. The sun’s rays warm the earth’s surface. A part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere due to the presence of gases like water vapour, carbon dioxide, methane, nitrous oxide etc known as greenhouse gases. This is known as the greenhouse effect. As you move further in this section you will learn about different gases that cause global warming. Excessive use of CFC’s damages ozone layer which protects the earth from harmful UV rays emitted by the sun.

Section 18.5 – Now you will study the measures that can prevent air pollution. There are many success stories in our fight against air pollution. For example, a few years ago, Delhi was one of the most polluted cities in the world. A decision was taken to switch to fuels like CNG and unleaded petrol. These measures have resulted in cleaner air for the city. Switching to alternative fuels, like solar energy, hydropower and wind energy, planting trees, use of fuels like CNG in automobiles, travelling to school on a bicycle or on public transport, avoiding the burning of leaves, trash and vegetable matter, restricting cigarette smoking are some of the measures that you can take to prevent and avoid air pollution.

Section 18.6 – In this section, you will study water pollution. In the first section of this chapter, you have already studied pollutants. Water pollution is the contamination of water by objectionable and harmful pollutants such as sewage, toxic chemicals, silt, etc. Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water. Water which is purified and fit for drinking is known as potable water. Water is a precious natural resource. We must learn to conserve it.

Section 18.7 – This section will teach you the causes of water pollution through a case study. The substances which contaminate the water are called water pollutants. Ganga is one of the most famous rivers in India. Millions of people depend on it for their daily needs. Recently a study by WWF ( World Wide Fund for Nature ) found that Ganga is one of the ten most endangered rivers in the world. An ambitious plan to save the river called the Ganga Action Plan was launched in 1985. Objectionable and harmful pollutants such as sewage, toxic chemicals, silt, etc. are responsible for the contamination of water. Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water.

Section 18.8 – This section will brief you about the potable water and how is water purified. Water which is purified and fit for drinking is known as potable water. Water is a precious natural resource. We must learn to conserve it. Let us see how water can be made safe for drinking: You have already seen how water is filtered. This is a physical method of removing impurities. A popular household filter is a candle type filter. Many households use boiling as a method for obtaining safe drinking water, Boiling kills the germs present in the water. Chlorination can also be used. It is a commonly used chemical method for purifying water.

Section 18.9 – Now you will study the measures that can prevent water pollution. Reduce, reuse and recycle should be our mantra!. Laws for industrial units should be strictly implemented so that polluted water is not disposed of directly into rivers and lakes. Water treatment plants should be installed in all industrial areas. At our individual levels, we should consciously save water and not waste it. We can think of creative ideas like reusing water used for washing and for other household tasks.

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