The correct option is (a).
Explanation
Acid rain refers to precipitation (rain, snow, fog, or hail) that is unusually acidic, meaning it possesses elevated levels of hydrogen ions (low pH). It is primarily a consequence of atmospheric pollution where specific gases react with water, oxygen, and other chemicals to form mild solutions of sulfuric and nitric acid.
Statement-wise Analysis:
- Statement 1 is Correct. Acid rain is caused by the emission of sulphur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. These gases react with water molecules, oxygen, and other oxidants in the presence of sunlight to form sulphuric acid (H2SO4) and nitric acid (HNO3), which then fall to earth as acid rain.
- Statement 2 is Incorrect. The burning of fossil fuels like coal and diesel is a combustion process that consumes oxygen. It releases carbon dioxide (CO2), sulphur dioxide (SO2), nitrogen oxides (NOx), and particulate matter. It does not release oxygen; rather, oxygen is a reactant required for the burning process.
- Statement 3 is Incorrect. Petrol engines burn hydrocarbon fuels. The exhaust from these engines contains a mixture of gases, primarily carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), and unburnt hydrocarbons, in addition to water vapour. Water vapour is not the only exhaust gas produced.
Key Takeaway:
Acid rain is an environmental phenomenon resulting from the chemical transformation of sulphur dioxide (SO2) and nitrogen oxides (NOx) emissions into acidic compounds within the atmosphere.