Q.1 What are the different ways in which water gets contaminated?
Sol. The different ways in which water gets contaminated are as follows:
(i) Many industries discharge harmful chemicals into rivers and streams. Examples are oil refineries, paper factories, textile and sugar mills, etc.
(ii) The pesticides and weedicides used for the protection of crops get dissolved in water and are washed into water bodies from the fields.
(iii) Many times untreated sewage is thrown directly into rivers.
(iv) Faecal matters of mammals get added into water bodies.

Q.2 At an individual level, how can you help reduce air pollution?
Sol. At an individual level, one can do following things to reduce air pollution:
(i) One can use vehicles consuming fuels like CNG and unleaded petrol, rather than those using fuels like diesel, petrol, etc.
(ii) One can avoid unnecessary usage of vehicles. And try using public transport more.
(iii) One can avoid using crackers.
(iv) One can generate awareness about air pollution among friends and neighbours.
(v) One can switch over to alternative fuels instead of the fossil fuels for energy requirements. These could be solar energy, hydropower and wind energy.
(vi) One can plant trees and nurture those trees already present in the neighbourhood.
(vii) Dry leaves can be burnt in a compost pit rather than burning in open.

Q.3 Clear, transparent water is always fit for drinking. Comment.
Sol. Clear, transparent water is not always fit for drinking. This is because the water which looks clean might contain disease-carrying microorganisms and dissolved impurities in it. These microorganisms and impurities could be harmful to us. Hence, it is essential to purify water before drinking.

Q.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.
Sol. Following is a list of measures that would help a town to ensure the supply of clean water to all its residents:
(i) Implementation of strict laws for industrial units so that the polluted water is not disposed off directly into rivers and lakes. Because it is same water we receive at our home.
(ii) Treatment of water must be done to make it free from harmful germs, chemicals and impurities.
(iii) The water supply pipes must be properly maintained to avoid any corrosion, breakage and leakage.
(vi) Campaigns and awareness programmes should be organized to keep water resources clean and educate people to save water.

Q.5 Explain the differences between pure air and polluted air.
Sol. Pure air: It is a mixture of gases which contains about 78% nitrogen, 21% oxygen and rest consists of carbon dioxide, argon, methane, ozone and water vapour. Such air is good for living being.
Polluted air: It is the air which is contaminated by unwanted substances which have a harmful effect on both the living and the non-living.

Q.6 Explain circumstances leading to acid rain. How does acid rain affect us?
Sol. Chemicals like sulphur dioxide and nitrogen dioxide are released into the air. These pollutants reacts with the water vapour present in the air and forms sulphuric and nitric acid. When it rains, these acids are present in it. Such kind of rain is called Acid Rain.
Following is list which shows how acid rain affect us:
(i) It can cause skin irritation.
(ii) It removes nutrients like calcium from the soil.
(iii) It causes corrosion to bridges, building and other metallic objects.
(iv) It can destroy plants and aquatic life.

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

Q.8 Describe the ‘Green House Effect’ in your own words.
Sol. ‘Green House Effect’ is the trapping of radiations inside the earth’s atmosphere. Along with other gases, CO₂ also gets trapped in the atmosphere which is mainly responsible for Greenhouse Effect. Because of human activities the amount of CO₂ level has increased in the atmosphere which traps heat and does not allow heat to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.

Q.9 Prepare a brief speech on global warming that you have to make in your class.
Sol. The continuous increase in the temperature of the earth is called Global Warming. Various gases like carbon dioxide, nitrous oxide, methane, etc. lead to this effect. But, the main contributor of global warming is Carbon dioxide. It traps the heat and does not allow it to escape into space. As a result, the average temperature of Earth is increasing. There are many effects of global warming like it can cause sea levels to rise dramatically. Moreover, it could result in wide ranging effects on rainfall patterns, agriculture, forests, plants and animals. Hence, we need to take steps to minimize it. It cannot be solved by the effort of only one country, it needs global effort of all countries to reduces its effects and completely eliminate it.

Q.10 Describe the threat to the beauty of the Taj Mahal.
Sol. Chemicals like sulphur dioxide and nitrogen dioxide are released into the air. The pollutants reacts with the water vapour present in the air and forms sulphuric and nitric acid. When it rains, these acids are also present. Such kind of rain is called Acid Rain. Acid rain can be harmful for living beings and also for non-living things. Acid rain corrodes the outer surface of buildings. This has caused the Taj Mahal becoming pale. The Acid rain has corroded the marble of this monument. And this phenomenon is called “Marble cancer”. In fact, suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards yellowing of the marble.

Q.11 Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Sol. The pesticides and weedicides used for the protection of crops get dissolved in water and are washed into water bodies from the fields. These acts as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. In this process a lot of oxygen in these ponds gets used up. This results in a decrease in the oxygen level, which kills aquatic organisms.