Question

____________ is a colorless, odorless gas that forms when fuels are not completely burned.

Answer 1

Your answer is Carbon monoxide

Answer 2

Explanation:

Carbon monoxide is a toxic and flammable gas which is also colorless. Chemical formula of carbon monoxide is CO.

This gas is produced upon incomplete combustion of carbon.

For example, $C(s) + \frac{1}{2}O_{2}(g) \rightarrow CO(g)$

Therefore, we can conclude that carbon monoxide is a colorless, odorless gas that forms when fuels are not completely burned.