The correct option is (b).
Explanation
Acid rain refers to any form of precipitation with acidic components, such as sulfuric or nitric acid, that fall to the ground from the atmosphere. While normal rain has a pH of about 5.6 due to dissolved carbon dioxide, acid rain typically has a pH value below 5.6.
Statement-wise Analysis
- Statement 1 is Incorrect. Acid rain is characterized by an excess of acids (hydrogen ions), not bases. It occurs when pollutants like sulphur dioxide and nitrogen oxides react with water, oxygen, and other chemicals to form sulfuric and nitric acids.
- Statement 2 is Correct. Acid rain has detrimental effects on the ecosystem. It damages the protective waxy coating on leaves, inhibits photosynthesis, and leaches essential nutrients from the soil. In aquatic environments, it lowers the pH of water bodies, which can be fatal to fish and other aquatic life.
- Statement 3 is Incorrect. Sulphur dioxide ($SO_2$) dissolves in rainwater and undergoes oxidation to form Sulphuric acid ($H_2SO_4$), not Hydrochloric acid. Similarly, Nitrogen oxides ($NO_x$) react to form Nitric acid ($HNO_3$). These are the two primary acids responsible for acid rain.
Key Takeaway: Acid rain is caused primarily by the emissions of Sulphur dioxide ($SO_2$) and Nitrogen oxides ($NO_x$), which react with atmospheric moisture to form Sulphuric acid and Nitric acid, respectively, lowering the pH of precipitation below 5.6.