Chapter 18 Pollution of Air and Water solution Exercise
1. What are the different ways in which water gets contaminated?
Answer
Water gets contaminated by the addition of:
→ Agricultural chemicals: Farmers use excessive amounts of pesticides and fertilizers to increase crop production. These chemicals get carried away to the water bodies due to rains and floods which lead to water pollution.
→ Industrial wastes: Industries release harmful chemical wastes into water sources, thereby polluting them.
→ Sewage wastes: Waste materials from kitchens, toilets, and laundry sources are also responsible for contaminating water.
2. At an individual level, how can you help reduce air pollution?
Answer
An individual can reduce air pollution by:
→ Avoiding the use of cars as much as possible and by using public transport whenever possible.
→ By not using vehicles for short distances.
→ By using clean fuels such as LPG and CNG instead of diesel and petrol.
→ Always disposing the garbage properly and not burning it.
→ Controlling the emissions from vehicles and household chimneys.
3. Clear, transparent water is always fit for drinking. Comment.
Answer
Clear and transparent water is not always fit for drinking. Water might appear clean, but it may contain some disease causing micro-organisms and other dissolved impurities. Hence, it is advised to purify water before drinking. Purification can be done by water purifying systems or by boiling the 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
To ensure the supply of clean water to all residents the following steps must be taken:
→ Leakages in pipelines of water should be repaired.
→ The main water source must be built in clean surroundings and should be maintained properly.
→ Open defection in water resources by slum dwellers should be strictly prohibited.
→ Chemical methods such as chlorination must be used for purifying water.
5. Explain the differences between pure air and polluted air.
Answer
| Pure Air | Polluted air |
| Pure air contains around 78% nitrogen, 21% oxygen, and 0.03% carbon dioxide also small amounts of argon, methane, ozone, and water vapours. | Polluted air includes gases like sulfur dioxide, nitrogen dioxide, carbon dioxide, etc. and other particulate matter. |
| Smog is not present. | Smog can be present. |
| Not harmful for human beings | Harmful for human beings as cause diseases like asthma |
6. Explain circumstances leading to acid rain. How does acid rain affect us?
Answer
When harmful gases like sulphur dioxide and nitrogen dioxide, react with moisture present in air, they form nitric acid and sulphuric acid. These acids when drop down on earth along with rain, is called acid rain.Effects of acid rain:
→ Acid rains damage crops, decrease fertility of soil and affect aquatic life.
→ Acid rains corrode buildings and structures.
7. Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen
► (d) Nitrogen
Page No: 253
8. Describe the ‘Greenhouse Effect’ in your own words.
Answer
The greenhouse effect is the rise in the temprature of the Earth’s surface due to increased concentration of greenhouse gases like carbon dioxide, methane, and water vapour in the atmosphere. These gases trap solar radiations released back by the Earth. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an increase in the Earth’s temperature leading to global warming.
9. Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer
Global warming is one of the greatest challenges that our planet is facing. It is the unequivocal and continuing rise in the average temperature of the Earth’s climate system. It occurs as a result of an increased concentration of greenhouse gases in the atmosphere. These gases trap solar radiations released back by the Earth. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an increase in the Earth’s temperature leading to global warming.
10. Describe the threat to the beauty of the Taj Mahal.
Answer
Acid rain is a major threat to the beauty of the Taj Mahal. When acid rains fall on the monument made of marble, they react with marble to form a powder-like substance that is then washed away by the rain. This phenomenon is known as marble cancer. Also, the soot particles emitted from the Mathura oil refinery located near Agra is leading to the yellowing of the marble.
11. Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer
The increased in the level of nutrients in the water leads to an excessive increase in the population of algae in the water body. When these algae die, they serve as food for decomposers. A lot of oxygen is utilised in this process, consequently leading to a decrease in the level of oxygen dissolved in the water body. This in turn causes fishes and other aquatic organisms to die.
Go Back To NCERT Solutions for Class 8 Science
Chapter 18 Pollution of Air and Water Class 8 Science NCERT Solutions
Detailed explanation provided under each NCERT solutions for Class 8 Science will help in understanding the concepts better. These NCERT Solutions are curated by the experts in a comprehensive which can be helpful in clearing your doubts instantly. It will be useful in analyzing the problems and answering it with precision and the right concepts.
Class 8 Science Chapter 18 Pollution of Air and Water NCERT Questions and Answers – Topics
• Air Pollution
• How does Air Get Polluted?
• Case Study – The Taj Mahal
• Greenhouse Effect
• What can be Done?
• Water Pollution
• How does Water Get Polluted?
→ Case Study
• What is Potable Water and How is Water Purified?
• What Can be Done?
Chapter 18 Pollution of Air and Water NCERT Solutions for Class 8 Science – Notes
• Pollution is the introduction of harmful or poisonous substances into environment that have adverse
effects on lives.
• When air is contaminated by unwanted substances which have a harmful effect on both the living and the non-living, it is referred to as air pollution.
• The substances which contaminate the air are called air pollutants.
→ The sources of air pollutants are factories, power plants, automobile exhausts and burning of firewood and dung cakes.
• Smog is made up of smoke and fog. Smoke may contain oxides of nitrogen which combine with other air pollutants and fog to form smog. The smog causes breathing difficulties such as asthma, cough and wheezing in children.
→ Other kinds of pollutants are chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays.
• Experts have warned that pollutants in air are discolouring Taj Mahal’ white marble.
→ The industries located in and around Agra like rubber processing, automobile, chemicals and especially the Mathura oil refinery, have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide.
→ The corrosion of the Taj Mahal due to acid rain is called ‘marble cancer.’
• Global warming has resulted in a rise in the global sea level. Gases, like methane, nitrous oxide and water vapour, also contribute to the greenhouse effect, and, along with carbon dioxide, are collectively called the greenhouse gases.
→ Many countries have reached an agreement to reduce the emission of greenhouse gases. The Kyoto Protocol is one such agreement.
• Steps to prevent air pollution:
→ Use of fuels like CNG and unleaded petrol in automobiles.
→ Switching to alternative fuels, like solar energy, hydropower and wind energy.
→ Planting more and more trees.
→ Use of public transport or car pooling.
→ Avoiding the burning of leaves, trash and vegetable matter.
→ Restricting cigarette smoking.
• Whenever harmful substances such as sewage, toxic chemicals, silt, etc., get mixed with water, the water becomes polluted. The substances that pollute water are called water pollutants.
• Ganga is one of the most famous rivers of India. It sustains most of the northern, central and eastern Indian population.
→ The pollution levels have been rising for many years due to quantities of garbage, untreated sewage, dead bodies, and many other harmful things, directly into the river.
→ The river is ‘dead’ at many places where the pollution levels are so high that aquatic life cannot survive.
→ The Ganga Action Plan was launched in 1985 which aimed to reduce the pollution levels in the river.
→ The Government of India has launched a new initiative known as National Mission for Clean Ganga (NMCG) in 2016.
• Water which is suitable for drinking is called potable water.
• Ways of making water potable are:
→ Using candle type water filters
→ Boiling
→ Chlorination
Chapter 18 Pollution of Air and Water Class 8 Science Questions and Answers – MCQ Questions with answers
1. Water pollution is caused by
a) Aquatic animals living in water
b) Excess drawing of water from water bodies
c) Plant growing near water bodies
d) Addition of untreated sewage in water bodies
► d) Addition of untreated sewage in water bodies
2. The process of waste treatment is called
a) Pollutant separation
b) Sewage treatment
c) Water treatment
d) Chlorination
► b) Sewage treatment
3. What is the effect of sulphur dioxide present in air on human beings?
a) Harms the skin and the lungs
b) Mixes with the blood and prevents it from carrying oxygen
c) Affects the heart and the liver
d) Raises the air temperature
► a) Harms the skin and the lungs
4. Which is not produced by burning of fossils fuel?
a) Carbon dioxide
b) Oxygen
c) Nitrogen oxide
d) Sulphur dioxide
► b) Oxygen
5. The Taj Mahal is being affected due to:
a) Noise pollution
b) Air pollution
c) Water pollution
d) None of the above
► b) Air pollution
6. Which one is not a natural source of water
a) Pond
b) Canal
c) River
d) Lake
► b) Canal
7. What is smog?
a) A combination of fire and water.
b) A combination of smoke and fog.
c) A combination of water and smoke.
d) A combination of air and water.
► b) A combination of smoke and fog.
8. Addition of harmful substance in water to make it unfit for human consumption is called
a) Water pollution
b) Biomagnifications
c) Decomposition
d) Retardation
► a) Water pollution
9. From which of the following bad effects does the ozone layer in our atmosphere protect us?
a) Carbon dioxide
b) CFC’s
c) The sun’s ultraviolet rays
d) All of the above
► c) The sun’s ultraviolet rays
10. The purest form of water is
a) Spring water
b) Subsoil water
c) Hand pump water
d) Rain water
► d) Rain water
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