Acid Rain from Nitrogen Dioxide Erodes Marble

Steps:

• Internal combustion engines emit CO, NOx (including NO and NO2), and hydrocarbons.
• Marble statues are made of calcium carbonate (CaCO3), which dissolves in acidic solutions.
• Acid rain forms when certain emissions react with atmospheric water to produce acids.
• Nitrogen dioxide (NO2) specifically contributes to nitric acid (HNO3) formation, accelerating marble erosion.

Why C is correct:

• Nitrogen dioxide (NO2) reacts with water vapor and oxygen to form nitric acid (HNO3) via 4NO2 + O2 + 2H2O → 4HNO3, which acidifies rain and dissolves CaCO3 in marble.

Why the others are wrong:

• A. Carbon monoxide (CO) is a toxic gas but does not form acids that erode marble.
• B. Nitrogen oxide (NO) oxidizes to NO2 but does not directly produce significant acid rain.
• D. Unburnt hydrocarbons contribute to smog and ozone but not to acid formation affecting marble.

Final answer: C