Answer: C. A catalytic converter in a car exhaust converts two combustion pollutants — carbon monoxide and nitrogen oxides — into harmless products in a single redox step:
\(2\text{NO} + 2\text{CO} \rightarrow \text{N}_2 + 2\text{CO}_2\).
CO is oxidised to \(\text{CO}_2\) (carbon goes from +2 to +4); NO is reduced to \(\text{N}_2\) (nitrogen goes from +2 to 0). Both happen on the same platinum/rhodium catalyst surface.
A reverses combustion (decomposition of \(\text{CO}_2\)) — not what a converter does. B forms NO at high engine temperatures, increasing pollution. D decomposes \(\text{NO}_2\) without dealing with CO.
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