Two undesirable products of incomplete combustion are:

The correct choice identifies carbon monoxide and aldehydes as undesirable products of incomplete combustion. Incomplete combustion occurs when there is insufficient oxygen available to completely oxidize the fuel, leading to the formation of harmful byproducts.

Carbon monoxide is a colorless, odorless gas that is highly toxic. It is produced when carbon-containing fuels do not burn completely. Inhalation of carbon monoxide can lead to serious health issues, including headaches, dizziness, and even death, as it interferes with the body's ability to transport oxygen.

Aldehydes, on the other hand, are carbonyl compounds that can also be products of incomplete combustion. They can contribute to air pollution and have harmful health effects, including respiratory problems and potential carcinogenic effects.

The other choices presented involve either products that are not typically associated with incomplete combustion or that are not inherently toxic or undesirable in the context of combustion byproducts. For example, carbon dioxide is a common product of complete combustion and is not considered undesirable in the same context as carbon monoxide and aldehydes.