The correct option is (c).
Explanation
Acid Rain refers to precipitation containing elevated levels of hydrogen ions (low pH). While normal rainwater is naturally slightly acidic due to the presence of dissolved carbon dioxide, acid rain is characterized by a pH significantly lower than 5.6, resulting from the presence of stronger acids.
- Statement 1 is Incorrect: Normal rain has a pH of about 5.6 because carbon dioxide ($CO_2$) in the atmosphere dissolves in it to form weak carbonic acid ($H_2CO_3$). The phenomenon of "Acid Rain" is not primarily caused by $CO_2$, but by the dissolution of sulfur and nitrogen oxides which form much stronger acids.
- Statement 2 is Correct: Acid rain causes significant damage to both ecological and man-made systems.
- Soil: It increases soil acidity, leaching away essential nutrients like calcium and magnesium, and mobilizing toxic metals such as aluminum, which harms plant roots.
- Buildings: It corrodes infrastructure, particularly structures made of limestone and marble (calcium carbonate). The reaction converts calcium carbonate into calcium sulphate, leading to the peeling and erosion of stone surfaces, often termed "Stone Leprosy."
- Statement 3 is Correct: The primary precursors of acid rain are sulfur dioxide ($SO_2$) and nitrogen oxides ($NO_x$). These pollutants are emitted from burning fossil fuels, volcanic eruptions, and vehicles. In the atmosphere, they react with water, oxygen, and other chemicals to form sulfuric acid ($H_2SO_4$) and nitric acid ($HNO_3$).
Key Takeaway: Normal rain is slightly acidic due to Carbon Dioxide. Acid rain is distinctively caused by Sulfur Dioxide ($SO_2$) and Nitrogen Oxides ($NO_x$), which create strong acids capable of damaging soil chemistry and corroding marble structures.