Question

what is always true of a combustion reaction? oxygen gas must be one of the reactants carbon monoxide will be produced the reaction absorbs energy one reactant must contain chlorine

Answer 1

Answer: A. Oxygen gas must be one of the reactants

Explanation: Properties of combustion reactions, whether inorganic or organic.

Answer 2

The correct answer should be
carbon monoxide will be produced

Combustions release heat, they don't absorb it. Oxygen is not necessary as other gasses can also do it, while chlorine is not necessary.