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

Chapter 18 - Pollution of Air and Water

Question 1: What are the different ways in which water gets contaminated?
Answer:
The different ways in which water gets contaminated are:
• Industrial waste: Industries release the harmful chemical wastes into water sources which makes the water polluted.
• Sewage waste: The kitchen, laundry and toilets wastes release the waste materials in the water and this makes the water polluted.
• Agricultural chemicals: Farmers use excessive amount of pesticides and fertilizers for enhancing crop production. Rains and floods carry these harmful chemicals to water bodies, which results in water pollution.

Question 2: At an individual level, how can you help reduce air pollution?
Answer:
At an individual level, we can help reduce air pollution by following ways:
• We should walk for shorter distances.
• We should avoid travelling unnecessarily.
• We should plant more trees.
• We should pollution check the vehicles.
• We should avoid the usage of personal cars and instead use public transport.
• We should buy lesser things that are manufactured using fossil fuels.

Question 3: Clear, transparent water is always fit for drinking. Comment.
Answer:
No, this statement is wrong because water might appear clean but it may contain some disease-causing microbes and other dissolved impurities. Therefore, we should purify the water by boiling or by any other method 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.
Answer:
The following measures can be taken by us to ensure the supply of clean water to our town residents:
• We should make sure that the water pipes are clean and no garbage is lying near water bodies.
• The wells and tube-wells should be made so that the rain water gets stored in it.
• Chemical methods like chlorination etc can be done to clean water for drinking and other purposes.

Question 5: Explain the differences between pure air and polluted air.
Answer:

• Pure air consists of 78% nitrogen, 21% oxygen, 0.03% carbon dioxide and other gases like methane, argon, ozone and water vapour which are present in very small amounts.
• Air is said to be polluted when there is the addition of few gases like sulphur dioxide, carbon monoxide, nitrogen dioxide etc.

Question 6: Explain circumstances leading to acid rain. How does acid rain affect us?
Answer:
Few gases like sulphur dioxide, nitrogen dioxide etc react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain. Acid rain can affect us in the following ways:
• It can destroy the crops.
• It can lead to marble cancer affect the monuments like Taj Mahal etc. Acid rain corrodes the marble of the monument. The phenomenon is also called ‘Marble cancer’.

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

Question 8: Describe the ‘Green House Effect’ in your own words.
Answer:
The greenhouse effect can increase in the temperature of the Earth. This is also known as Global Warming. The greenhouse gases cause the greenhouse effect. Few greenhouse gases are methane, carbon dioxide, sulphur dioxide. When these radiation reach the Earth, they get absorbed by the Earth and then released back to the atmosphere. Greenhouse gases present into the atmosphere trap these radiations and do not allow the heat to leave. This makes the Earth warm and therefore the life is present. But, due to sudden increase in level of greenhouse gases, can lead to an excessive increase in the Earth’s temperature leading to global warming.

Question 9: Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer:
Global warming is the term used to describe the rising average temperature on the Earth. In other words, it’s the process in which the entire planet is heating up. The factors responsible for the change in climate is a phenomenon known as greenhouse effect. The industrial revolution humans have been burning large amounts of fossils fuel such as oil and gas producing huge clouds of carbon dioxide. The gases released into the atmosphere during this process act like an invisible blanket trapping the heat from the Sun and warming the Earth. This is known as the “Greenhouse effect”.  Not only is that deforestation another huge reason for global warming. Trees absorb huge amounts of carbon dioxide from the air and release oxygen back into it so due to a decrease in the number of trees and forests the carbon dioxide remains in the atmosphere adding fuel in the fire and warming the globe. We can reduce global warming by trying to switch your normal bulb with energy-saving light-bulb, take a walk or bicycle instead of using car for a shorter distance. Always turn off the electrical items when we’re not using them and most importantly recycle and reduce your food wastage.

Question 10: Describe the threat to the beauty of the Taj Mahal.
Answer:
The pollutants in air are discolouring Taj Mahal’s white marble. The industries located in and around Agra like automobile, Mathura oil refinery etc have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide. These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain. Acid rain corrodes the marble of the monument. The phenomenon is also called “Marble cancer”. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards the yellowing of the marble.

Question 11: Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer:
The increased level of nutrients in the water can affect the survival of aquatic organisms because due to an increase in the level of nutrients in water can increase the population of algae in the water. When these algae die, they serve as food for decomposers. A lot of oxygen is utilized in this process, leading to a decrease in the level of oxygen dissolved in the water body and this causes aquatic organisms to die.

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