Compound Q is acetaldehyde, reacting with both Tollen's and iodoform reagents

Steps:

• Tollen's reagent oxidizes aldehydes to carboxylic acids, forming a silver mirror; positive test confirms -CHO group.
• Alkaline I₂(aq) performs iodoform test, yielding yellow precipitate for acetaldehyde (CH₃CHO) or methyl ketones (CH₃CO-).
• Q positive for both tests must be an aldehyde with CH₃CHO structure, excluding simple aldehydes or ketones.
• Among options, only acetaldehyde fits both criteria exactly.

Why C is correct:

• CH₃CHO (acetaldehyde) has -CHO for Tollen's oxidation and CH₃CHO for iodoform halogenation to CHI₃.

Why the others are wrong:

• A: CH₃CH₂CHO (propanal) gives Tollen's but not iodoform, lacking CH₃CO- or CH₃CHO structure.
• B: CH₃COCHO (methylglyoxal) is α-keto aldehyde; gives both but structurally complex, not simple match.
• D: CH₃COCH₃ (acetone) gives iodoform as methyl ketone but not Tollen's, lacking -CHO.

Final answer: C