What are the products of complete combustion of hydrocarbons?

• A. Carbon dioxide and water.
• B. Oxygen gas and water.
• C. Carbon monoxide and water.
• D. Soot and water.

Answer: (A)

Complete combustion of hydrocarbons happens when there is plenty of oxygen, so every carbon in the molecule is oxidized to carbon dioxide and every hydrogen becomes water. The general idea is that the hydrocarbon plus oxygen yields carbon dioxide and water, since combustion is the oxidation of fuel. That’s why carbon dioxide and water are the products you’d expect under proper burning conditions.

The other possibilities would indicate incomplete combustion or an unusual scenario: carbon monoxide or soot appears when oxygen is limited, not when it’s abundant, and oxygen gas would not be produced during burning.