Important Questions Class 8 Science Chapter 18

Important Questions Class 8 Science Chapter 18 – Pollution of Air and Water.

Science is a subject that requires both academic study and practical implementation. The eighteenth chapter of the Class 8th CBSE Science curriculum is about “Pollution of Air and Water. This chapter discusses how our environment is being affected by our day-to-day activities. The key topics covered in this chapter are:

  • air pollution.
  • Case Study: The Taj Mahal
  • greenhouse effect.
  • water pollution.
  • What is potable water?
  • How is water purified?

At Extramarks, we understand the value of practising important questions to master the main concepts. We have created multiple study resources, such as NCERT solutions, chapter-wise notes, CBSE revision notes, etc., to help students with their studies. Students can check our question bank of Important Questions for Class 8 Science Chapter 18, which has been compiled by experts who meticulously pick questions from various sources such as the NCERT textbook, NCERT exemplar book, other Science reference books, CBSE past years’ question papers, etc. The step-wise explanations for each question help students revise the entire chapter while solving these questions. Students can register themselves on Extramarks’ website to access all the Important Questions for Class 8 Science Chapter 18.

Get Access to CBSE Class 8 Science Important Questions 2022-23 with Chapter-Wise Solutions

You can also find CBSE Class 8 Science Chapter-by-Chapter Important Questions here:

CBSE Class 8 Science Important Questions
Sr No. Chapters Chapters Name
1 Chapter 1 Crop Production and Management
2 Chapter 2 Microorganisms : Friend and Foe
3 Chapter 3 Synthetic Fibres and Plastics
4 Chapter 4 Materials : Metals and NonMetals
5 Chapter 5 Coal and Petroleum
6 Chapter 6 Combustion and Flame
7 Chapter 7 Conservation of Plants and Animals
8 Chapter 8 Cell Structure and Functions
9 Chapter 9 Reproduction in Animals
10 Chapter 10 Reaching The Age of Adolescence
11 Chapter 11 Force and Pressure
12 Chapter 12 Friction
13 Chapter 13 Sound
14 Chapter 14 Chemical Effects of Electric Current
15 Chapter 15 Some Natural Phenomena
16 Chapter 16 Light
17 Chapter 17 Stars and The Solar System
18 Chapter 18 Pollution of Air and Water

Important Questions Class 8 Science Chapter 18- with Solutions

Science in secondary school becomes extensive with chapters from Physics, Chemistry, and Biology. And students should have a strong grip on this subject as Classes 8, 9, and 10 will form the foundation for Classes 11 and Class 12 Science.

One of the most important aspects of learning subjects like Science is to practise a lot of questions.Students can confidently depend on our Extramarks question bank containing Class 8 Science Chapter 18 Important Questions, created by experienced Science faculty , after analysing all past papers and textbook questions. It’s a comprehensive bunch of questions which cover the entire syllabus. Chapter 18: Class 8 Science Important Questions is a tool that students can use to improve their competency and score.

The following are some questions and answers from our question bank for Science Class 8 Chapter 18 Important Questions:

Question 1. What is potable water?

Answer 1. Water which is good enough for drinking purposes is called potable water.

Question 2. Write two ways by which water can be made safe for drinking.

Answer 2. Ways through which water can be made safe for drinking:

  1. Boiling
  2. Filtration
  3. Chlorination

Question 3. What is air pollution?

Answer 3. When air is contaminated by unwanted substances harming both the living and the non-living, it is called air pollution. Substances which pollute the air are known as air pollutants. It is an undesirable change in the atmosphere and can cause diseases in humans, animals and plants.

Question 4. What is acid rain?

Answer 4. The sulphur dioxide and nitrogen dioxide in the air, which are released from various factories, combine with the water vapour in the atmosphere to form sulphuric acid and nitric acid. These acids drop down with rain, which is called acid rain. Acid rain can be harmful to both living and non-living beings. .

  1. It may cause rashes, itching, and other skin problems in humans.
  2. Acid rain damages plant leaves.
  3. It also causes the yellowing of various monuments.
  4. It makes sea/river water unfit for aquatic animals.

Question 5. What causes the increasing amount of carbon dioxide in the air?

Answer 5. Various causes lead to the increase in carbon dioxide in the atmosphere-

  1. Burning of fossil fuels at a very high rate in factories.
  2. Carbon ejection by vehicles.
  3. Deforestation.

Question 6. Define water pollution.

Answer 6. The addition of unwanted and harmful substances in the water, which makes it unsuitable for drinking and other purposes, is known as water pollution. Substances which pollute water are called water pollutants. Polluted water increases the risk for aquatic animals to survive as the pH and temperature of water change. It also increases algae’s growth, reducing oxygen levels in water bodies.

Question 7. What are the different ways by which water gets contaminated?

Answer 7. The different ways by which the water gets contaminated are-

  1. i) Industrial waste- The harmful chemical wastes get released by the industries into water sources.
  2. ii) Sewage waste- kitchen, laundry, and toilets release the waste materials, polluting the water.

iii) Agricultural chemicals- Farmers use excessive pesticides and fertilisers to enhance crop production. Rains carry these harmful chemicals to water bodies, which results in water pollution.

Question 8. As an individual, how can you help reduce air pollution?

Answer 8.  We can take the following steps to reduce air pollution:

  1. i) We should avoid using personal vehicles and use public transport as much as possible. Carpooling is another good option for working professionals.
  2. ii) We should dispose of the garbage properly and not burn it.

iii) For shorter distances, avoid using vehicles. One can walk or cycle to nearby places.

  1. iv) We should control the number of waste from household chimneys and vehicles.
  2. v) We should replace our automobile fuel, diesel and petrol with LPG and CNG.
  3. vi) Use eco-friendly carry bags instead of polythene bags.

Question 9. Write a short note about the Ganga Action Plan.

Answer 9. Ganga Action Plan is a plan to conserve the river Ganga launched in the year 1985. It is aimed at reducing the pollution levels in the Ganga river which has become one of the ten most endangered rivers in the world. However, the increasing urbanisation and industrialisation have already damaged the river beyond repair. The Government of India launched a new National Mission for Clean Ganga (NMCG) initiative in 2016.

Question 10. Describe the greenhouse effect.

Answer 10. A greenhouse effect is an event in which the sun’s rays are captured and absorbed by the greenhouse gases such as carbon dioxide, CFCs etc., which increases the earth’s temperature.

Question 11. What is global warming?

Answer 11. The gradual increase in the earth’s temperature due to the release of methane, carbon dioxide and chlorofluorocarbons (CFCs) which causes the greenhouse effect, is called global warming. The harmful effects of global warming include

  1. Threat to aquatic life
  2. Flooding
  3. Loss of habitation for both marine animals as well as human beings.

Question 12. What are some of the sources of air pollution?

Answer 12. Some sources of air pollution are as follows-

  1. Carbon dioxide is released from industries and vehicles.
  2. Forest fire
  3. Burning of firewood and dung cakes.
  4. Storms.
  5. Mining activities.

Question 13. How do environmental problems affect people’s health?

Answer 13. Environmental problems can cause various physical, biological and chemical hazards in humans due to air, water, or soil pollution. Some of them are listed below:

  1. Respiratory diseases like asthma and bronchitis.
  2. Cancer.
  3. Heart diseases.
  4. Water-borne diseases like diarrhoea.

Question 14. Clear transparent water is suitable for drinking. Comment. 

Answer 14. No, clear and transparent water is not  always good for drinking. There are possibilities of disease-causing microbes and dissolved impurities in the clear and transparent water, which are not visible to the naked eye. So, it is necessary to purify water before drinking. Water can be filtered by using water purifiers, chlorination or boiling.

Question 15. Explain the threat to the beauty of the Taj Mahal.

Answer 15. The major threat to the Taj Mahal is acid rain. When the acid rain falls on the monument, which is completely made of marble, they react with marble to form a powdery substance which is then washed away along with the rain. This phenomenon is known as marble cancer. In addition, the soot particles from the Mathura oil refinery near Agra led to the yellowing of the Taj Mahal marble.

Question 16. Why does the increased nutrients level in the water affect the survival of aquatic 


Answer 16. An increase in the nutrient level in the water body leads to an excessive rise in the population of algae in the water bodies. When these algae perish, they serve as food for decomposers. A bulk of oxygen is utilised in this process, decreasing the oxygen level dissolved in the water body. This, in turn, causes fish and aquatic organisms to die.

Question 17. What do CFCs stand for? Name some devices where CFCs are used. Why are CFCs considered pollutants?

Answer 17. CFCs stand for chlorofluorocarbons. CFCs are used in devices like refrigerators, air conditioners etc. CFCs are considered pollutants because they deplete the ozone layers present in the atmosphere. This results in the entry of harmful radiation from the sun.

Question 18. Why is it advised that industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra?

Answer 18. Industries and factories should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra because using fossil fuels releases sulphur-di-oxide gas into the atmosphere. This mixes with rainwater to convert to sulphuric acid, causing acid rain. Acid rains affect the white marble of the Tajmahal and turn  them  yellow.

Question 19. It is said that “CO2 contributes to global warming.” Explain.

Answer 19. CO2 is constantly being released by human activities. CO2 is a harmful gas that contributes to air pollution and global warming.    Plants utilise CO2 from the atmosphere for the photosynthesis process, thereby reducing the amount of CO2 in the air. The  area under forest cover is decreasing, due to human activities and industrialisation. Deforestation increases the amount of CO2 in the air because the number of trees that consume CO2 is reduced. Human activities, therefore, contribute to the accumulation of Carbon dioxide in the atmosphere. CO2 traps heat and does not allow this heat to escape into space, thereby raising the average temperature of the earth’s atmosphere is increasing slowly and contributing to global warming.

Question 20. We should plant trees and nurture the ones present already in the neighbourhood. Why?

Answer 20. We should plant as well as nurture the existing trees in the neighbourhood because plants consume CO2 and thus reduce atmospheric CO2 content. Thus they will help in reducing  global warming and its consequences.

Question 21. What is the traditional way of purifying water to make it fit for drinking?

Answer 21. Filtration:

This is a physical method of removing impurities. A popular household filter is a candle-type filter.

Boiling- Many households use boiling as a traditional method for obtaining safe drinking water.

Chlorination- Chlorination is a commonly used chemical method for filtering water. It is done by applying chlorine tablets or bleaching powder to  water.

Question 22. How can we reuse, reduce and recycle water?

Answer 22. Reduce- While brushing your teeth, leaving the tap running may waste several litres of water. A tap drips once every second and wastes a few thousand litres of water yearly.

Reuse- Water used for washing vegetables may be used to water plants in the garden.


Dirty water can be recycled after purification.

Benefits of Solving Important Questions Class 8 Science Chapter 18

Students can face problems understanding the new and challenging concepts in science. One way to solve this is to practise questions from our question bank of Important Questions for Class 8 Science Chapter 18. Class 8 Science (Chapter 18)Important Questions cover all the topics from the chapter, and these questions are created from an exam point of view, which is what is expected in the exams. Solving these important questions gives students an extra boost during their exams and helps them get excellent scores.

Here are some benefits of referring to and solving questions from our question set of Important Questions for Class 8 Science Chapter 18:

  • Comprehensive sets of questions are included from authentic sources such as the NCERT textbook, NCERT exemplar, other science reference books, and many CBSE past exam papers. So students don’t have to waste their time by referring to multiple sources to revise the same syllabus. In our Important Questions Class 8 Science Chapter 18, they get access to a variety of exam-oriented questions and give them added confidence to get a 100% score.
  • For each question, there is a step-by-step and a self-explanable solution given by our experienced science faculty. This helps students to evaluate and understand their strengths and weaknesses. It gives a deep understanding of concepts and helps them prepare for their exams in a balanced manner.
  • The list of Important Questions for Class 8 Science Chapter 18 consists of a variety of question formats, such as objective types, short , and long answers. This gives students exposure to different types of questions that are usually expected in the exams. This will help students to frame the right answers quickly and be confident.
  • Students can get detailed and accurate solutions to questions given in the NCERT textbook, which will help them understand how to solve the different kinds of problems in a step-by-step manner. If they ever get stuck on a question, they can always refer to the solutions prepared by subject matter experts.

Extramarks believes in incorporating the best learning experiences through its own repository. To enjoy the maximum benefit of these resources, students just need to register themselves at Extramarks.

website and stay ahead of the competition. Students can find various study materials which they can refer to based on their requirements.

Extramarks is one of the leading online platforms that offers comprehensive learning solutions to students in classes 1–12. We also provide additional study and course materials. Students can also click the links below to access the most important resources.

  • NCERT books
  • CBSE Revision Notes
  • CBSE syllabus
  • CBSE sample papers
  • CBSE past years’ question papers
  • Important formulas
  • CBSE extra questions

Q.1 Answer the following questions:
i. Which chromosome pair in humans is different than the others?
ii. How is a human zygote formed?
iii. How many chromosome pairs are present in a zygote?


i. The twenty-third chromosome pair (XX/XY) in humans differs from the others. This last pair specifies whether the person is male or female.
ii. A human zygote is formed when a male gamete containing either X or Y chromosome fuses with a female gamete containing an X chromosome.
iii. A zygote has 23 pairs of chromosomes, that is a total of 46 chromosomes.

Q.2 Answer the following questions:
i. Which chromosome pair in humans is different than the others?
ii. How is a human zygote formed?
iii. How many chromosome pairs are present in a zygote?


i. The twenty-third chromosome pair (XX/XY) in humans differs from the others. This last pair specifies whether the person is male or female.
ii. A human zygote is formed when a male gamete containing either X or Y chromosome fuses with a female gamete containing an X chromosome.
iii. A zygote has 23 pairs of chromosomes, that is a total of 46 chromosomes.

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FAQs (Frequently Asked Questions)

1. Is the list of Important Questions Class 8 Science Chapter 18 enough to score good marks?

The solutions we provide here are concise and written from an examination perspective. The answers to the exercise questions are clearly explained with examples. They are 100% accurate. These answers will help students prepare for the exam as we strictly follow the guidelines provided by the NCERT book and the CBSE Science syllabus. The solutions thus provided assist students develop conceptual clarity by explaining the key concepts in an easy-to-comprehend language. This exercise covers all the topics and subtopics that your Class 8 Science exams could be expected to cover.

However, we also recommend that students study the official NCERT textbooks and exemplars along with our study resources.

2. Which important chapters are included in the Class 8 Science syllabus?

The CBSE Class 8 Science syllabus contains a total of eighteen chapters. All eighteen chapters are important both for enhancing knowledge and from an exam point of view. So, we suggest students fully prepare for these chapters.

Here  is a list of 18 chapters:

Chapter 1    Crop Production and Management

Chapter 2    Microorganisms: Friend and Foe

Chapter 3    Synthetic Fibres and Plastics

Chapter 4    Materials: Metals and Non-Metals

Chapter 5    Coal and Petroleum

Chapter 6    Combustion and Flame

Chapter 7    Conservation of Plants and Animals

Chapter 8    Cell – Structure and Functions

Chapter 9    Reproduction in Animals

Chapter 10    Reaching the Age of Adolescence

Chapter 11    Force and Pressure

Chapter 12    Friction

Chapter 13    Sound

Chapter 14    Chemical Effects of Electric Current

Chapter 15    Some Natural Phenomena

Chapter 16    Light

Chapter 17    Stars and The Solar System

Chapter 18    Pollution of Air and Water