LiAlH4 reduces multiple carbonyls to alcohols in M

Steps:

• M is a C3 compound with a ketone and carboxylic acid, like pyruvic acid (CH3COCOOH, C3H4O3).
• Excess LiAlH4 reduces the ketone to a secondary alcohol (CH3CH(OH)-).
• LiAlH4 then reduces the carboxylic acid to a primary alcohol (-CH2OH).
• Dilute acid workup yields the diol CH3CH(OH)CH2OH (C3H8O2).

Why D is correct:

• Full reduction of both carbonyls in a β-keto acid adds four hydrogens, matching the diol formula C3H8O2.

Why the others are wrong:

• A: C3H6O is a monohydric alcohol or carbonyl, missing one oxygen from incomplete reduction.
• B: C3H6O2 resembles the unsaturated or unreduced dicarbonyl starting material.
• C: C3H8O is a single alcohol from reducing only one carbonyl group.

Final answer: D