The correct answer is Sulphur dioxide and Nitrogen oxides. Explanation & Key Takeaways: • Acid rain is caused mainly due to the presence of Sulphur dioxide (SO₂) and Nitrogen oxides (NOₓ) in the atmosphere. These gases react with water, oxygen, and other chemicals to form acidic compounds like sulfuric acid (H₂SO₄) and nitric acid (HNO₃). • These acidic compounds mix with rainwater and fall to the earth in the form of acid rain. This phenomenon significantly affects ecosystems, buildings, and human health. • Sulphur dioxide is primarily released from the burning of fossil fuels such as coal and oil at power plants and industrial facilities. • Nitrogen oxides are mainly emitted from vehicles, industrial processes, and power generation. • Acid rain is harmful as it leads to the acidification of water bodies, damages forests, corrodes buildings and monuments, and depletes soil nutrients. Related Concepts: • Sources of Sulphur Dioxide and Nitrogen Oxides: • Sulphur Dioxide: Emissions are largely from burning fossil fuels (coal and oil), industrial processes like smelting, and natural sources like volcanic eruptions. • Nitrogen Oxides: Emissions come from vehicle exhausts, industrial processes, and power plants. Natural sources include lightning and microbial processes in soils. • Effects of Acid Rain: • Acid rain lowers the pH of lakes and rivers, making them uninhabitable for aquatic life. • It damages vegetation by leaching essential nutrients from the soil and weakening plants. • It causes corrosion of historical monuments and buildings, such as the Taj Mahal in India. • Acid rain can have adverse effects on human health by causing respiratory issues due to inhalation of fine acidic particles. • Prevention and Control Measures: • Reduction in the use of fossil fuels and adoption of cleaner energy sources like solar, wind, and hydropower. • Implementation of technologies like scrubbers in industrial plants to reduce SO₂ emissions. • Promotion of public transportation to reduce vehicle emissions of NOₓ. • International agreements like the Convention on Long-Range Transboundary Air Pollution (CLRTAP) aim to reduce acid rain-causing emissions globally. Important Notes: • The pH level of normal rainwater is around 5.6 due to the presence of dissolved carbon dioxide. Acid rain typically has a pH below 4.5. • The phenomenon of acid rain was first discovered by the Scottish chemist Robert Angus Smith in 1852. • Regions affected by acid rain include industrial areas of the United States, Europe, and parts of Asia.