- A Carbon dioxide gradually dissolving in rainwater to form a mild carbonic acid solution
- B SO2 and NOx from burning fossil fuels dissolving in rain to form sulphuric and nitric acids
- C Methane in the atmosphere slowly reacting with moisture present in the stratosphere
- D Ozone depletion gradually allowing excess UV radiation to reach low-level rainclouds
Correct answer: B. SO2 and NOx from burning fossil fuels dissolving in rain to form sulphuric and nitric acids
Explanation: Acid rain forms when SO2 (from power plants, industries) and NOx (from vehicles) react with water in the atmosphere: SO2 + H2O → H2SO3 (sulphurous acid); 2NO2 + H2O → HNO3 + HNO2. Normal rain pH ~5.6; acid rain pH < 5.6. Damages forests, aquatic life, and buildings.
Concept context
Pollution, global warming, ozone depletion, deforestation, and sustainability. Important for NEET and general awareness.