Answer: D (redox). In a catalytic converter the harmful gases carbon monoxide and nitrogen monoxide are converted into the less harmful gases carbon dioxide and nitrogen: \(2\text{CO} + 2\text{NO} \to 2\text{CO}_2 + \text{N}_2\). The carbon in CO is oxidised from +2 to +4, while the nitrogen in NO is reduced from +2 to 0. Because something is oxidised and something is reduced at the same time, this is a redox reaction.
The other options do not fit. Combustion involves burning a fuel in oxygen, which is not what happens here. Evaporation is a change of state, and precipitation is the formation of an insoluble solid from solution — neither applies to a reaction between gases.
The reaction is best described as redox, so the answer is D.
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