Question

1. choose the best answer. what phase of matter are all the compounds in for this reaction? gas liquid solid

Explanation:

Assuming the reaction in context (like many common gas - phase reactions, e.g., reactions of gaseous compounds like $\ce{H_{2}}$, $\ce{O_{2}}$, $\ce{CO_{2}}$ etc.), if all compounds are in gas phase, the best answer is gas. The options are gas, liquid, solid. Since the selected option is gas, and typically in many chemical reactions (like combustion, synthesis of gaseous products) compounds are gaseous.

Answer:

A. gas