GSEB Class 8 Science Solutions Chapter 18 Pollution of Air and Water

Question 1. What are the different ways in which water gets contaminated?
Answer: Water becomes impure in the following ways:
1. Many industries release harmful chemicals into rivers and streams.
2. Water gets spoiled when sewage is dumped into rivers.
3. Pesticides, weedicides, and other chemicals also dissolve in water, making it dirty.
4. Microorganisms growing in water also make it polluted.
In simple words: Water gets dirty when factories pour chemicals, sewage goes into rivers, farm chemicals mix in, and tiny living things grow in it.

Exam Tip: Remember to list at least four distinct sources of water contamination, such as industrial waste, sewage, agricultural runoff, and biological growth, to score full marks.

Question 2. At an individual level, how can you help reduce air pollution?
Answer: We can reduce air pollution through these actions:
1. We should plant more trees to lower the amount of carbon dioxide and lessen air pollution.
2. By using CNG and unleaded petrol in our vehicles.
3. By using public transport as much as possible.
4. By creating general awareness about air pollution among our family and friends.
In simple words: Individuals can help by planting trees, using cleaner vehicle fuels like CNG, taking public transport, and teaching others about air pollution.

Exam Tip: When discussing individual actions, focus on practical, daily habits like tree planting, fuel choices, and public transport use, as well as community awareness.

Question 3. Clear, transparent water is always fit for drinking. Comment.
Answer: Clear, transparent water is always suitable for drinking. This statement is incorrect because many tiny living things (microorganisms) can be present in it. So, we should cleanse it by boiling.
In simple words: Clear water isn't always safe to drink because unseen germs might be present. It's important to boil it to make it clean.

Exam Tip: Highlight that clarity doesn't equal purity. Emphasize the hidden dangers of microorganisms and the importance of purification methods like boiling.

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.
Answer: A list of actions that would help our town ensure the provision of clean water to all its residents:
1. Proper cleaning of the water tank.
2. Chlorine tablets should be made available.
3. To get clean water in every household, it is essential that water reaching the houses undergoes treatment.
In simple words: To provide clean water to everyone, our town should clean water tanks, offer chlorine tablets, and treat water before it reaches homes.

Exam Tip: When detailing municipal measures, include infrastructure maintenance (tanks), purification methods (chlorine), and water treatment at the source.

Question 5. Explain the differences between pure air and polluted air.
Answer: Pure air is free from germs and harmful gases. It contains 78% nitrogen, 21% oxygen, and a small amount of other gases and dust particles.
Polluted air contains harmful gases and unwanted substances.
In simple words: Pure air is clean, with mostly nitrogen and oxygen, no bad gases or germs. Polluted air has unhealthy gases and dirt.

Exam Tip: Clearly state the composition of pure air (main gases and percentages) and contrast it with polluted air by mentioning harmful gases and unwanted substances.

Question 6. Explain circumstances leading to acid rain. How does acid rain affect us?
Answer: Some pollutants, like sulphur dioxide and nitrogen dioxide, interact with the water vapour present in the atmosphere to create sulphuric acid and nitric acid. These acid drops then fall down with rain, making the rain acidic. This process is called acid rain. Acid rain affects us in many ways:
1. Acid rain harms the marble of monuments.
2. Acid rain damages building and sculptural materials.
3. Acid rain also spoils freshwater.
4. Acid rain also harms our crops and makes them poisonous.
5. Acid rain damages the leaves of plants.
In simple words: Acid rain happens when pollutants like sulphur and nitrogen oxides mix with water in the air, forming acids that fall as rain. It harms buildings, water, crops, and plants.

Exam Tip: In your explanation, identify the key pollutants (sulphur dioxide, nitrogen dioxide) and their reaction with water vapor. List specific impacts on both living and non-living things.

Question 7. Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen.
Answer: (d) Nitrogen.
In simple words: Carbon dioxide, sulphur dioxide, and methane are all greenhouse gases, but nitrogen is not.

Exam Tip: Memorize the common greenhouse gases (e.g., carbon dioxide, methane, nitrous oxide, water vapor) to easily identify non-greenhouse gases like nitrogen.

Question 8. Describe the 'Greenhouse Effect' in your own words:
Answer: When sunlight reaches the earth, some of the radiation that hits the earth is taken in by it, and some is sent back into space. A part of the reflected radiation gets trapped by the atmosphere. This trapped radiation further makes the earth warmer. This process is known as the Greenhouse effect. Too much carbon dioxide in the air is one of the gases responsible for this effect.
In simple words: The Greenhouse Effect is when the Earth's atmosphere traps some of the sun's heat, making the planet warm. Too much CO2 in the air makes this effect stronger.

Exam Tip: Clearly explain the balance between absorbed and reflected solar radiation, and how specific gases (like CO2) contribute to trapping heat in the atmosphere, leading to warming.

Question 9. Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer: The steady rise in the earth's temperature is called global warming. There are many causes for it. One of them is an increase in human population. A rise in the number of vehicles is also one of the reasons. Air pollution has also increased global warming. Cutting down trees and animals grazing on plants also contribute to global warming.
In simple words: Global warming means the Earth's temperature is always getting higher. This happens because of more people, more cars, air pollution, cutting down trees, and animals eating too many plants.

Exam Tip: For a speech on global warming, focus on defining it, then list human activities (population growth, vehicles, deforestation, pollution) that contribute to the issue. Keep it concise and impactful.

Question 10. Describe the threat to the beauty of the Taj Mahal.
Answer: Over the last two decades, India's most famous tourist spot, the Taj Mahal in Agra, has become a concern. Experts have warned that air pollution is causing its white marble to lose color. So, it's not only living things but also non-living things like buildings, monuments, and statues that are affected by polluted air.
The industries located in and around Agra, such as rubber processing, automobiles, chemicals, and especially the Mathura Oil Refinery, have been accountable for producing pollutants like sulphur dioxide and nitrogen dioxide. These gases react with water vapor present in the atmosphere to create sulphuric acid and nitric acid. These then fall with the rain, creating acid rain.
This is called acid rain. Acid rain has led to the corrosion of the monument's marble. This phenomenon is also called "Marble cancer". Suspended particulate matter, such as the soot particles released by the Mathura Oil Refinery, have also caused the marble to turn yellow.
The Supreme Court has taken steps to preserve the Taj. It has directed industries to switch to cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas). Additionally, vehicles should switch to unleaded petrol in the Taj zone.
In simple words: The Taj Mahal's marble is being harmed by air pollution, turning it yellow. Industries around Agra, especially the Mathura Oil Refinery, release chemicals that cause acid rain, corroding the marble, a problem called "Marble cancer." The Supreme Court has ordered cleaner fuels for industries and vehicles to protect it.

Exam Tip: To describe the threat to the Taj Mahal, mention air pollution causing discoloration, acid rain from industrial emissions (sulphur and nitrogen dioxide), and the specific term "Marble cancer." Also, include the protective measures taken by authorities.

Question 11. Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer: Too many chemicals get washed away from farm fields. These chemicals act as food for algae to grow rapidly. Once these algae die, they become food for decomposers like bacteria. A lot of oxygen in the water then gets used up. This results in a drop in the oxygen level, which can kill aquatic organisms.
In simple words: Extra nutrients from farms make too much algae grow. When algae die, bacteria use up a lot of oxygen in the water while breaking them down. This lack of oxygen then kills fish and other water animals.

Exam Tip: When explaining this process, use keywords like "excess nutrients," "algal bloom," "decomposition," "oxygen depletion," and "aquatic life" to show a clear understanding of eutrophication.