Question 1. State the different ways in which water is contaminated.
Solution :
The different ways in which the water is contaminated are :
(i) Industrial waste: The harmful chemical wastes, released by the industries into water sources and pollutes the water.
(ii) Sewage waste: kitchen, laundry and toilet release the waste materials that are responsible for polluting water.
(iii) Agricultural chemicals: Excessive amount of pesticides and fertilizers are used by the farmers for enhancing crop production. Rains and floods contain harmful chemicals carried away to water bodies and pollute the water.

Question 2. What are the steps you could take to reduce air pollution?
Solution :
The following are the steps taken for reduction of air pollution:
i) We should avoid the usage of personal cars and opt public transport as much as possible.
ii) We should properly dispose the garbage and not burn it.
iii) For shorter distances, avoid vehicles.
iv) We should control the amount of emissions from household chimneys and vehicles.
v) We should replace our vehicle fuel, diesel and petrol by LPG and CNG.

Question 3. Do you agree that clean, transparent water is always fit for drinking?
Solution : No, we don’t agree to the statement that clean water is always fit for drinking because water might appear clean but it may contains some disease causing micro-organisms and several other dissolved impurities. Hence, we advised to purify the water by boiling or by any purifying system before drinking it.

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.
Solution :
The following steps could be taken:
(a) First of all, procurement of required amount of water for all residents should be ensured.
(b) Wastage of water by leakage at various places should be taken into account.
(c) Water treatment should be ensured.
(d) Must have sufficient water tanker to meet emergency situations.

Question 5. Explain the differences between pure air and polluted air.
Solution : Pure air is free from any pollutant, has no smell, is soothing and not irritating to eyes. Whereas polluted air gives a filthy smell and people cannot breathe in it. If people inhale such air, they may suffer from various breathing, heart and lung problems. Even sometimes people die inhaling polluted air.

Question 6. Explain circumstances leading to acid rain. How does acid rain affect us?
Solution : Gases like sulphur dioxide and nitrogen dioxide react with water vapour present in atmosphere to form Sulphuric acid and nitric acid. These acids come down with rain water, making the rain acidic. This is known as acid rain.
Acid rain corrodes the marbles of the monuments. This phenomenon is known as Marble Cancer. It also kills the useful organism in agricultural soil.

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

Solution : (d) Nitrogen

Question 8. Describe the ‘Green House Effect’ in your own words.
Solution : ‘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.

Question 9. Prepare a brief speech on global warming that you have to make in your class.
Solution : 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.

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

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

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