Identifying methyl ketone via selective chemical tests

Steps:

• Tollen's reagent test negative: X lacks aldehyde group, eliminating A (CH3CHO).
• Yellow precipitate with alkaline I2(aq): Positive iodoform test indicates methyl ketone (or acetaldehyde/alcohols oxidizing to them), but prior step rules out aldehyde.
• No reaction with sodium: X lacks -OH group, eliminating D (CH3CH2OH) which evolves H2.
• Thus, X matches methyl ketone structure, which is B (CH3COCH3).

Why B is correct:

• CH3COCH3 (acetone) is a methyl ketone with CH3-C=O group, yielding CHI3 precipitate in iodoform reaction per haloform mechanism.

Why the others are wrong:

• A: CH3CHO (acetaldehyde) reduces Tollen's to silver mirror.
• C: CH3COOCH3 (methyl acetate) is ester, inert to iodoform test.
• D: CH3CH2OH (ethanol) reacts with Na to form H2 gas.

Final answer: B