Catalytic converters target nitrogen oxides to curb acid rain

Steps:

• Acid rain forms from gases like sulfur dioxide and nitrogen oxides (NOx) reacting with water to create acids.
• Car exhaust contains NOx, primarily nitrogen dioxide (NO2), from high-temperature combustion.
• Catalytic converters use platinum and other metals to reduce NOx to harmless nitrogen gas (N2) and oxygen (O2).
• Among options, only nitrogen dioxide fits as a NOx gas removed this way and linked to acid rain.

Why D is correct:

• Nitrogen dioxide (NO2) dissolves in rainwater to form nitric acid (HNO3), directly causing acid rain; catalytic converters reduce it via 2NO2 + 2CO → 2CO2 + N2.

Why the others are wrong:

• A. Carbon dioxide causes global warming via greenhouse effect, not acid rain.
• B. Carbon monoxide is oxidized to CO2 in converters but forms carbonic acid weakly, insufficient for acid rain.
• C. Hydrocarbon vapours contribute to smog and ozone, not acid rain; converters break them into CO2 and H2O.

Final answer: D