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

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

Answer: Ways due to which water gets polluted are –

• Excess use of chemical fertilisers in fields contaminate groundwater. Also, if these chemicals are carried ways due to floods or any other reason then it contaminates other water resources.
• Passing industrial waste into sources of water causes contamination.
• Wastewater from houses when passed to the sources of water causes its contamination.

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

Answer: Air Pollution can be reduced as –

• Use public transport and avoid use of personal vehicles
• Use bicycle instead of bike for short distances
• Use of CNG rather and petrol or other polluting fuels
• Do not burn the garbage, instead use proper disposal method

3. Clear, transparent water is always fit for drinking. Comment.Answer: No, clear transparent water is not always fit for drinking. It can contain microbes causing diseases or impurities, that could be bad for health. Therefore, it always advice to boil water and use or use a water purifier to get pure water.

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.

Answer: Following measures should be taken to ensure the supply of clean water –

• Water storage or water source for the town should be in clean surrounding.
• For purifying water chemical methods like chlorination should be used
• Water pipes should be installed in clean area.
• Water storage tanks should be kept clean

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

Answer: Pure air contains nitrogen (78%), oxygen (21%), carbon dioxide (0.03%) and other gases like argon, methane, ozone, etc. When there is addition of other component like carbon monoxide, sulphur dioxide, etc in the air, then the air is said to be polluted.

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

Answer: When fossil fuels are burned they release sulphur dioxide in the air. Sulphur dioxide reacts with water vapours thereby forming sulphuric acid and nitric acid. When these acids comes down from rain it is called acid rain. Acid rain damage crops in the fields. It damages building and construction. Taj Mahal is one of the example of damage caused by acid rain.

7. Which of the following is not a greenhouse gas?

(a) Carbon dioxide

(b) Sulphur dioxide

(c) Methane

(d Nitrogen

Answer: (d Nitrogen

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

Answer: Greenhouse effect increases the average temperature of earth thereby causing global warming. It is caused by greenhouse gases like carbon dioxide, methane, water vapour, etc. Radiations from sun are partially absorbed by the earth and partially reflected back. Greenhouse gases trap these radiations and thus do not allow the heat to leave from earth’s atmosphere. This keeps the temperature of plant balanced and facilitating the survival of life. However, if these is increase in amount of these gases, more heat will be trapped in the atmosphere, thereby increasing temperature of earth causing global warming.

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

Answer: Global warming is caused due to increasing in average temperature of earth. It is caused by greenhouse gases like carbon dioxide, methane, water vapour, etc. Radiations from sun are partially absorbed by the earth and partially reflected back. Greenhouse gases trap these radiations and thus do not allow the heat to leave from earth’s atmosphere. This keeps the temperature of plant balanced and facilitating the survival of life. However, if these is increase in amount of these gases, more heat will be trapped in the atmosphere, thereby increasing temperature of earth causing global warming.

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

Answer: Acid rain is the threat to the beauty of Taj Mahal. Acids from acid rain reacts with marble of the Taj Mahal. Thus, it forms powder like substance which gets washed away due to rain. Also, soot particles from factories causes yellowing of marble.

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

Answer: Increase in level of nutrients causes bloom of algae. This breaks the contact of sunlight and water, causing harm to aquatic life. Also, when algae die, the act as food for decomposers. This process utilise more oxygen, thus decreasing level of oxygen in water. This causes death of aquatic organisms.

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Download free NCERT textbook class 8 Science – Chapter 18 Pollution of Air and Water