Which of the following is not a product of incomplete combustion of the engine?

Carbon dioxide is not a product of incomplete combustion; rather, it is a product of complete combustion. When fuel burns completely, it reacts with oxygen to produce carbon dioxide and water as the primary byproducts. This reaction indicates that all the fuel has been fully oxidized.

In contrast, carbon monoxide, unburned hydrocarbons, and soot are all indicative of incomplete combustion. In these situations, not enough oxygen is present, or the combustion process is inefficient, leading to the formation of these harmful products. Carbon monoxide is a toxic gas produced when insufficient oxygen is available to allow fuel to combust fully. Unburned hydrocarbons are fuel particles that were not oxidized, while soot consists of carbon particles resulting from the burning of fossil fuels without adequate oxygen.

Therefore, carbon dioxide is aligned with complete combustion processes, confirming it is not a product of incomplete combustion.