NCERT Solutions Class 8 Science Chapter 18

NCERT Solutions for Class 8 Science Chapter 18

Science tries to offer accurate and precise explanations of how the natural world works, what its constituents are, and how the world came to be the way it is now. Science’s knowledge is constantly being questioned and revised. Why isn’t any scientific notion ever “proven” once and for all? Science is always looking for new data that may uncover flaws in our existing understandings.

Our surroundings have changed dramatically over the last few decades, and pollution is one of the most important contributing factors. NCERT Class 8 Science Chapter 18 is Pollution of Air and Water. First, we will have a look at air and water pollution. Pollutants are chemicals that pollute water and air, according to Class 8 Science Chapter 18. Natural sources of pollution generally include smoke and dust from forest fires and volcanic eruptions. Artificial breakdown consists of the power plant and automotive emissions and firewood burning. The primary air pollutants include carbon dioxide, carbon monoxide, nitrogen oxides, sulphur dioxide and methane. 

Extramarks’ website offers Class 8 Science Chapter 18 Solutions for students. These solutions help students grasp the root of the Chapter easily. Pollution of Air and Water Class 8 solutions help you learn the concepts through intensive answers to the NCERT questions and retain them. This is what makes Extramarks popular among students.

Extramarks can be a one-stop solution for all students’ problems. Apart from NCERT Solutions for Class 8 Science Chapter 12- Friction, NCERT Solutions for other subjects and chapters, Additional Questions, Sample Papers, Revision Notes, CBSE Previous year question papers, and a lot more can be found on the Extramarks website. 

Key Topics Covered in NCERT Solutions for Class 8 Science Chapter 18

Making it convenient for the students and listing below the key topics that are covered in NCERT Solutions for Class 8 Science Chapter 18:

Air Pollution
Taj Mahal and the effects of Air pollution
Global Warming
Water Pollution

Let us look at Extramarks’ in-depth information on each subtopic in NCERT Solutions for Class 8 Science Chapter 18- Pollution of Air and Water.


According to NCERT Solutions for Class 8 Science Chapter 18, Pollution refers to unfavorable changes in the environment that harm plants, animals, and other biological and physical components of the environment.

  • A pollutant is a chemical that creates pollution. Contaminants can exist as liquids, solids, or gases.
  • When the concentration of a material exceeds the natural abundance, it is classified as a pollutant. Human actions or natural phenomena might cause this increase in concentration
  • Pollution exists in all forms, viz. Air pollution, sound pollution, light pollution, water pollution, soil pollution, etc. 

This chapter mainly focuses on two fundamental types of Pollution- Water and Air. Hence, let us take a look at the importance of both Water and Air:


  • Streams, rivers, lakes, and the season of the earth’s crust are primary water sources.
  • It is essential for the survival of life on Earth.
  • It is used for agriculture, drinking, washing, cleaning, and other human activities. 


  • The presence of air in our life is unavoidable.
  • The creatures’ survival depends on the availability of oxygen in the air.
  • Their bodies use oxygen to make energy.

Air Pollution

Any physical, chemical or biological alteration in the air is air pollution. Air pollution occurs due to toxic gases, dust, and smoke which significantly impacts plants, animals, and humans.

Cause of Air Pollution

NCERT Solutions for Class 8 Science Chapter 18 briefs about the causes of Air Pollution:

  • Sulphur dioxide is produced in significant quantities when fossil fuels are burned. In addition, air pollution is caused by carbon monoxide generated by the incomplete combustion of fossil fuels.
  • Vehicles such as jeeps, trucks, cars , buses, and other automobiles generate gases that contaminate the environment. These are the primary contributors of greenhouse gases and cause sickness in people.
  • Ammonia is one of the most dangerous gases produced by agricultural operations. Insecticides, fertilisers and pesticides pollute the atmosphere by emitting toxic substances.
  • Carbon monoxide, hydrocarbons, organic molecules, and chemicals are primarily produced in factories and industries. These are discharged into the atmosphere, causing it to deteriorate.
  • The minerals under the earth’s surface are retrieved using enormous equipment during the mining operation. The dust and chemicals emitted during the process contaminate the air and harm the employees’ and residents’ health.
  • Toxic chemicals are released into the air through paints and household cleaning products which not only pollute the air but further make it difficult to breathe.

Effects of Air Pollution

  • In humans, it causes allergies, illnesses, and sometimes even death.
  • This causes birth abnormalities in newborns.
  • Endangers animal health, plant and vegetation wellbeing.

Air Pollutants

Air pollutants can be defined as compounds present in high concentrations in the air which can be harmful to all the organisms or materials exposed to the atmosphere.

Solid particles, liquid droplets, and gases may have the presence of air pollutants, according to NCERT Solutions for Class 8 Science Chapter 18.

Examples are methane, chlorofluorocarbons, particulate matter, sulphur dioxide, nitrogen dioxide, carbon monoxide, lead, and other pollutants.

Carbon dioxide and Carbon monoxide

Carbon dioxide is produced via cement manufacture, deforestation, and the combustion of fuels such as gasoline, natural gas, oil, coal, and wood.

Incomplete combustion of carbon-containing materials, especially fuels, is a source of carbon monoxide (a harmful air pollutant).

Sulphur and Nitrogen

Primary air pollutants are nitrogen dioxide (NO2) and sulphur dioxide (SO2). Petroleum refineries and power stations that use fossil fuels such as coal are sources.


  • Respiratory issues, including irreversible lung damage.
  • Acid rains. 
  • Photochemical haze, which makes it harder to breathe.

Particulate matter

Particulates are solid or liquid particles that stay suspended in air, water, or gas.

Dust, pollen, trash, soot, acid drops, and smoke are examples.

Construction, road dust, power plants, industry, deforestation, and agricultural operations are all causes.


  • Diseases of the lungs and heart
  • Asthma
  • Malformations during birth

The above section of NCERT Solutions for Class 8 Science Chapter 18 explains Air Pollution and its aspects in complete detail. For more information, refer to the Extramarks website. It is loaded with quality study material.


NCERT Solutions for Class 8 Science Chapter 18 explains that Smoke and fog combine to form Smog. There are two types of Smog- Classical and Photochemical Smog.

Classical Smog:

  • This form of Smog arises in humid environments with high levels of sulfur oxides in the air.
  • Smoke, fog, and mainly sulfur dioxide gas make up the combination.

Photochemical Smog:

  • Smog of this sort is common in locations with a dry, sunny atmosphere and many automobiles.
  • It is primarily generated by chemical reactions between sunlight and nitrogen oxides.

Effects of Smog:

  • Asthma, wheezing, and cough are some examples of breathing problems.
  • Damage to plant cells inhibits their development, resulting in a significant reduction in agriculture and forest destruction.
  • Construction Materials, metals, and painted surfaces corrode due to photochemical pollution.

Taj Mahal and the effects of Air pollution

Before going into the case study of the Taj Mahal, NCERT Solutions for Class 8 Science Chapter 18 explains what CFCs or Chlorofluorocarbons are. CFCs are chemical compounds made up of fluorine, chlorine, and carbon. CFCs are majorly employed in aerosol sprays and as refrigerants in air conditioners, freezers, and cooling plants.

CFCs deplete the ozone layer, which shields the planet from the sun’s ultraviolet radiation. Humans can get ailments such as eye damage, skin cancer, and immune system suppression due to increasing UV radiation.

Effects of air pollution on Taj Mahal

The acids, Carbonic acid, Nitric acid, and  Sulphuric acid are formed when carbon dioxide, sulfur dioxide, and nitrogen dioxide react with water vapor in the atmosphere.

Rain brings these acids down, making the environment acidic.

Involved reactions:

CO2(g) + 2H2O(I)= 2H2CO3(aq)

2SO2(g) + O2 + 2H2O(I)= 2H2SO4(aq)

4NO2 + O2(g) + 2H20(I)= 4HNO3(aq)


  • The monument’s marble is eroded by acid rain.
  • In addition, the white marble is becoming dark because of pollution.

Global Warming

NCERT Solutions for Class 8 Science Chapter 18 lands on one of the essential topics of the chapter’ Global warming’.

Greenhouse Gases

The gases that cause the greenhouse effect are referred to as greenhouse gases. Water vapour, nitrous oxide, carbon dioxide, and methane are examples of such greenhouse gases.

Greenhouse effect:

  • The majority of solar energy is absorbed by the atmosphere.
  • The surface of the planet radiates heat back into space.
  • A portion of it is trapped in the atmosphere by greenhouse gases.
  • This effect keeps the earth’s surface at a comfortable temperature.

Global Warming

Global warming is defined as the phenomenon of rising in the average temperature of the earth’s atmosphere caused by an abundance of greenhouse gases.

Deforestation, factories, oil refineries, power plants, excessive burning of fossil fuels such as natural gas, oil, and coal, and so on are all contributing factors.

Effects of Global Warming:

  • The earth’s temperature has increased on average throughout time.
  • Natural disasters like floods, cyclones, earthquakes, and other natural disasters are becoming more severe.
  • Due to global warming, the polar ice caps are melting and this has resulted in an increase in mean sea levels.
  • Climate patterns have been changing all across the world.

What can we humans do to Reduce Air Pollution?

NCERT Solutions for Class 8 Science Chapter 18 suggests some ways in which Air Pollution can be reduced:

  • Encourage the usage of compressed natural gas (CNG), which is a greener alternative to gasoline and diesel.
  • Unleaded gasoline can be used because it does not emit dangerous gases into the environment.
  • Maintain hygiene by properly disposing of waste to regions where it can be left, burnt, or safely disposed of.
  • Taking public transportation or carpooling is cost-effective, relieves traffic congestion, and reduces emissions significantly.

Water Pollution

Extramarks NCERT Solutions for Class 8 Science Chapter 18 explains Water Pollution in the following section. The contamination of water bodies with toxic waste is known as water pollution.


  • Industries
  • Agriculture
  • Urbanization
  • Religious and social customs

Water Pollutants

Water pollutants are compounds that contaminate the water. Detergents, hospital chemicals, insecticides and herbicides, to name a few.

Effects of water pollution on the holy river Ganga

  • Garbage, untreated sewage, corpses, and various other dangerous substances are dumped straight into the river by the people of towns and cities through which the river passes.
  • Pollution in the Ganga is suffocating aquatic life and stunting plant development.
  • The Ganga is one of the world’s ten most threatened rivers.

Potable and Raw Water

Potable water is water that is good for drinking. All pollutants and dangerous microorganisms are removed from the drinking water.

Raw water is water that is not potable or appropriate for consumption.

Ways to convert Raw to Potable Water.

Extramarks NCERT Solutions for Class 8 Science Chapter 18 states that the following are the ways to convert Raw water to Potable water:

Boiling Water:

  • All germs are killed by boiling the water.
  • It protects us from infections spread by water.

Filtering Water:

  • Removing suspended solid materials from a liquid is known as filtration.
  • To some extent, filtration may remove all bacteria and pollutants from water.


  • The water is chlorinated by adding chlorine pills or bleaching powder.
  • In tap water, this procedure destroys some bacteria and other germs.

NCERT Solutions for Class 8 Science Chapter 18 Exercise and Solutions

Studying the NCERT Solutions for any chapter is the most innovative way to grasp all of the concepts in that Chapter. Extramarks deliver NCERT Solutions for each Chapter as a bonus. Subject experts create these Solutions to meet all of the demands of the students. Click on the below links to view NCERT Solutions for Class 8 Science Chapter 18:

Class 8 Science Chapter 18: Very Short Answer Type Questions

Class 8 Science Chapter 18: Short Answer Type Questions

Class 8 Science Chapter 18: Long Answer Type Questions

Students may access NCERT Solutions for Class 8 Science Chapter 18 and other chapters by clicking here. In addition, students can also explore NCERT Solutions for other classes below.

By getting access to NCERT Solutions for Class 8 Science Chapter 18- Pollution of Air and Water, students can easily understand and retain all the answers of the NCERT questions given at the end of the Chapter 

NCERT Solutions Class 8 Science Chapter-wise List

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

Key Features of NCERT Solutions for Class 8 Science Chapter 18

To excel in the forthcoming examination, students are advised to go through the NCERT Solutions of each Chapter. So why should you choose Extramarks? Here’s why:

  • They consist of stepwise and detailed answers including various concepts covered in the Chapter.
  • Based on the NCERT standards, Extramarks has compiled the most relevant material on this topic. 
  • After studying these Solutions, students are instilled with confidence.

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


Water gets contaminated by following ways:

  1. Excessive amounts of pesticides and fertilisers are being used to increase crop production. These chemicals are carried away to the water bodies by rains and floods which contaminate water.
  2. Harmful chemicals discharged from industries pollute water bodies.
  3. Water gets contaminated by the discharge of sewage into rivers.

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


An individual can reduce air pollution by:

  1. Using public transport and encouraging car pooling.
  2. Using bicycle for short distances.
  3. Using CNG and unleaded petrol instead of leaded petrol and diesel in automobiles.
  4. Using alternative fuels like solar energy, wind energy and hydropower instead of fossil fuels.
  5. Planting trees and nurturing the ones already present.

Q.3 Clear, transparent water is always fit for drinking. Comment.


No, clear and transparent water is not always fit for drinking. Water which looks clean may still have disease carrying microorganisms and dissolved impurities. Therefore, it is essential to purify water before drinking.

Q.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.


As a member of the municipal body of my town, I would take certain necessary actions to ensure the supply of clean water.

  1. Water must be treated properly to make it fit for use.
  2. Chlorination must be done to disinfect the drinking water supplies.
  3. Rain water harvesting will be made mandatory in every house.

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


Pure air Polluted air
Pure air contains 78% nitrogen, 21% oxygen and 0.03% carbon dioxide. Water vapour and other gases are present in traces. Composition of air is altered by the presence of harmful substances such as oxides of nitrogen, sulphur dioxide, carbon monoxide, particulate matters, etc.
It does not have any harmful substances. Increased level of harmful substances and poisonous gases are present.
Pure air is fit for breathing and does not cause any respiratory problems. Polluted air is unfit for breathing and causes many respiratory problems like asthma.

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


Sulphur dioxide and oxides of nitrogen are produced from various industries. These gases react with water vapour present in the air to form sulphuric acid and nitric acid, respectively. These acids come down with the rain water and this process is called acid rain.

Acid rain destroys plants and vegetation. The water of the rivers and the lakes becomes acidic and this causes the destruction of the aquatic life. Acid rain also destroys the ancient buildings, monuments and sculptures due to the continuous erosion of the marble.

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

  1. Carbon dioxide
  2. Sulphur dioxide
  3. Methane
  4. Nitrogen


The correct options are (d).

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


Gases like carbon dioxide, methane, water vapour etc. present in the atmosphere are called green house gases. These gases trap the heat from Sun and prevent it from escaping into the outer space. It helps in keeping earth warm and is essential for life on earth. But increase in the concentration of these gases leads to excessive increase in Earth’s temperature leading to global warming.

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


Global warming is an increase in the average temperature of Earth’s atmosphere. It is caused due to increased levels of green house gases like carbon dioxide, oxides of nitrogen, water vapour, methane, etc. These gases absorb solar radiation and prevent it from escaping into the outer space thereby, increasing Earth’s average temperature.

This continuous warming has lead to an increase in the temperature of Earth’s surface by 0.6°C approx. in the last three decades. Due to a rise in the temperature, the polar ice is melting and is threatening the survival of the polar bears.

The melting of the polar ice causes a rise in the sea level. It harms the coastal life and vegetation.

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


Sulphur dioxide and nitrogen dioxide produced from the industries like rubber processing industry, Mathura oil refinery etc. located in and around Agra are responsible for the discolouring of white marble of Taj Mahal. Sulphur dioxide and nitrogen dioxide gases released from the industries, react with water vapour present in the air to form sulphuric acid and nitric acid, respectively. The acids drop down with rain, making rain acidic. Acid rain corrodes the marble of the Taj Mahal. The phenomenon is also known as ‘Marble Cancer’. Suspended particulate matters emitted by ‘Mathura oil refinery’ have also contributed towards the yellowing of the marble.

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


When water bodies are nutrient enriched, then a dense growth of algae occurs. When these algae die, the decomposers decompose them by using a lot of oxygen. It results in decrease in concentration of oxygen in water resulting in death of aquatic organisms.

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FAQs (Frequently Asked Questions)

1. What are the adverse outcomes of acid rain?

Acid rain occurs when rain-carrying pollutants such as nitrogen oxide and sulfur dioxide fall. Animals and plants living in water bodies and on land are affected by acid rain. The acidity of water rises as a result of the acid rain. It also causes damage to sculptures and structures.

2. Describe air. Mention the various components of philosophy and their names as per Class 8 Science Chapter 18?

Air is made up of numerous different gases. It is both odourless and undetectable. The following are the components of air: Oxygen, Nitrogen, Water vapour, Argon, Methane and Carbon Dioxide.