A mixture looks uniform and contains two gases. What is its most appropriate classification?

Correct answer: Gas in gas solution

A homogeneous mixture has a uniform composition throughout, and solution classification uses the states of the solute and solvent. Since both components in the question are gases, the appropriate classification is gas in gas. Liquid-in-gas would require a liquid solute, solid-in-gas a solid solute, and solid-in-solid two solid components. Therefore, A is correct.