CBSE Class 8 Science Chapter 18: Pollution of Air and Water NCERT Solutions

Solution: Water can become contaminated through several pathways:

1. Industrial Waste: Various industries release untreated waste containing poisonous chemicals directly into rivers and other water bodies. These chemicals pollute the water, making it harmful for consumption and aquatic life.

2. Sewage Disposal: Untreated sewage from households and urban areas is often discharged into rivers. This sewage contains human waste and other pollutants that contaminate the water.

3. Agricultural Runoff: Farmers use insecticides and pesticides to protect crops. When it rains, these chemicals can be washed into the soil and eventually mix with groundwater or surface water sources, contaminating them.

Solution: Individuals can significantly contribute to reducing air pollution through the following actions:

1. Plant Trees: Trees absorb pollutants like carbon dioxide from the air and release oxygen, thus purifying the air.

2. Use Public Transport and Carpool: Opting for public transportation or carpooling reduces the number of vehicles on the road, thereby decreasing emissions.

3. Choose Sustainable Commuting: For short distances, walking or cycling are excellent alternatives to using vehicles, as they produce no air pollution.

4. Avoid Burning: Refrain from burning garbage, dry leaves, or crackers. Burning releases harmful greenhouse gases and particulate matter into the atmosphere, contributing to global warming and respiratory problems.

Solution: The statement that clear, transparent water is always fit for drinking is incorrect. Water may appear clean and pure to the eye, but it can still contain harmful contaminants that are not visible. These can include:

1. Microorganisms: Disease-causing bacteria, viruses, and protozoa can be present in water even if it looks clear. These microorganisms can cause serious illnesses.

2. Dissolved Chemicals: Harmful chemicals from industrial or agricultural sources might be dissolved in the water, making it unsafe without treatment.

Therefore, it is essential to purify water before drinking, either by using a water purifier or by boiling it, to ensure it is free from harmful contaminants.

Solution: As a member of the municipal body, the following measures can be implemented to ensure a clean water supply for all residents:

1. Water Treatment Plants: Establish and maintain efficient water treatment plants to purify water, removing harmful germs, chemical impurities, and physical contaminants before distribution.

2. Regulation of Waste Disposal: Enforce strict laws requiring industries to treat their chemical waste before discharging it into water bodies. Also, ensure proper treatment of sewage before it enters natural water sources.

3. Pipe Maintenance: Regularly inspect and maintain the water supply pipes to prevent corrosion, leakage, or breakage, which can lead to contamination.

4. Source Protection: Protect water sources like rivers and lakes from pollution by preventing dumping of waste and controlling runoff from agricultural and urban areas.

5. Public Awareness Campaigns: Organize campaigns to educate residents about the importance of conserving water and keeping water resources clean. Encourage responsible water usage habits.

Solution: The difference between pure air and polluted air lies in their composition and effect on living beings:

Pure Air: Pure air is a mixture of gases present in their natural, healthy proportions. Typically, it consists of approximately 78% nitrogen, 21% oxygen, and small amounts of other gases like carbon dioxide, argon, methane, and ozone. This composition is essential and beneficial for the survival and well-being of living organisms.

Polluted Air: Polluted air is air that has been contaminated by unwanted and harmful substances. These contaminants, known as pollutants, can be in the form of gases, liquids, or solid particles. Polluted air has detrimental effects on both living beings (causing health problems) and the non-living environment (damaging buildings, affecting climate).

Solution:

Circumstances Leading to Acid Rain: Acid rain occurs when certain pollutants in the atmosphere react with water vapor. Primarily, harmful gases like sulphur dioxide (SO_2) and nitrogen dioxide (NO_2), released from the burning of fossil fuels (like coal and oil) and industrial processes, rise into the atmosphere. These gases react with water vapor (H_2O) present in the air to form weak solutions of sulphuric acid (H_2SO_4) and nitric acid (HNO_3). When this acidic water falls to the earth in the form of rain, snow, fog, or even dry particles, it is called acid rain.

Effects of Acid Rain: Acid rain has several adverse effects on the environment and living beings:

Health: It can cause skin irritation and respiratory problems in humans.

Plants: It inhibits the germination of seeds and damages plants, affecting crop yields and forest health.

Structures: Acid rain corrodes buildings, bridges, statues, and other structures made of stone and metal.

Soil and Water: It alters the fertility of the soil and changes the pH of lakes and rivers, harming aquatic life.