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

Solution: Water can become contaminated through several pathways:

1. Industrial Waste: Many industries release harmful chemicals and waste products directly into rivers and other water bodies. These toxic substances poison the water, making it unsafe.

2. Sewage Disposal: When sewage, which contains human waste and other pollutants, is discharged into water sources without adequate treatment, it contaminates the water with harmful microorganisms and organic matter.

3. Agricultural Runoff: Farmers often use insecticides and pesticides on their crops. When it rains, these chemicals can be washed off the fields and seep into the groundwater or flow into rivers, contaminating the water supply.

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

1. Plant Trees: Trees absorb pollutants like carbon dioxide 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. Walk or Cycle: For short distances, choosing to walk or cycle instead of using vehicles helps cut down on fuel consumption and air pollution.

4. Avoid Burning Waste: Burning garbage and dry leaves releases harmful greenhouse gases and particulate matter into the atmosphere, contributing to global warming and respiratory problems. It is better to compost or dispose of waste properly.

5. Say No to Crackers: Fireworks release a significant amount of pollutants into the air and also cause noise pollution. Avoiding them helps in reducing both types of pollution.

Solution: The statement that clear, transparent water is always fit for drinking is incorrect. Water may appear clean and pure to the naked eye, but it can still contain harmful contaminants. These can include:

1. Microorganisms: Invisible disease-causing bacteria, viruses, and protozoa can be present in water, leading to various illnesses.

2. Dissolved Chemicals: Harmful chemicals, heavy metals, or excessive salts might be dissolved in the water, which are not visible but can be detrimental to health.

Therefore, it is essential to purify water before drinking, either by using water purifiers 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. Effective Water Treatment: Implement and maintain advanced water treatment plants to remove harmful germs, chemical impurities, and physical contaminants from the water sources before distribution.

2. Pollution Control Laws: Enforce strict laws requiring industries to treat their wastewater and chemicals before discharging them into water bodies. This protects the raw water sources.

3. Infrastructure Maintenance: Regularly inspect and maintain the water supply pipes. Repair any leaks, corrosion, or breakages promptly to prevent contamination from entering the distribution system.

4. Awareness Campaigns: Conduct public awareness programs to educate residents about the importance of keeping water resources clean, proper waste disposal, and water conservation practices.

5. Monitoring Water Quality: Regularly test the water quality at various points in the supply system to ensure it consistently meets safety standards.

Solution: The key differences between pure air and polluted air are:

Pure Air: Pure air is a mixture of gases present in their natural proportions, which is essential for the survival of living beings. Typically, it consists of approximately 78% nitrogen, 21% oxygen, and very small amounts of other gases like carbon dioxide, argon, methane, and ozone, along with water vapor.

Polluted Air: Polluted air is air that has been contaminated by unwanted and harmful substances. These contaminants, often called pollutants, can be in the form of gases, liquids, or solid particles. Polluted air has detrimental effects on both living organisms (causing health problems) and non-living things (like damaging buildings and reducing visibility).

Solution:

Circumstances Leading to Acid Rain: Acid rain occurs when certain pollutants in the atmosphere react with water vapor. Specifically, harmful gases like sulphur dioxide (SO_2) and nitrogen dioxide (NO_2), released from the burning of fossil fuels and industrial processes, rise into the atmosphere. Here, they react with water vapor (H_2O) to form sulphuric acid (H_2SO_4) and nitric acid (HNO_3). These acids then fall to the Earth along with rain, snow, or fog, making the precipitation acidic. This phenomenon is known as acid rain.

Effects of Acid Rain: Acid rain has several adverse effects:

• On Humans: It can cause skin irritation and respiratory problems.
• On Plants: It inhibits the germination of seeds and can damage plant tissues, affecting crop yields and forest health.
• On Structures: Acid rain corrodes buildings, bridges, and statues made of materials like marble and limestone.
• On Soil and Water: It changes the fertility of the soil by leaching essential nutrients and can make lakes and rivers acidic, harming or killing aquatic life.