Ketone identification via carbonyl tests

Steps:

• Carbonyl compounds react with 2,4-DNP to form hydrazones, confirming aldehydes or ketones.
• Fehling's reagent oxidizes aldehydes but not ketones, so no reaction indicates no aldehyde.
• Combine these: positive 2,4-DNP and negative Fehling's prove ketone, excluding aldehydes.
• Other tests like Tollens' or iodoform distinguish further but aren't definitive alone.

Why C is correct:

• Ketones form orange 2,4-DNP precipitates (general carbonyl test) but resist Fehling's oxidation due to lacking aldehydic hydrogen (R-CO-R structure).

Why the others are wrong:

• A: No Tollens' rules out aldehydes, but iodoform reaction occurs with methyl ketones and some alcohols/aldehydes, not proving ketone.
• B: LiAlH4 reduces many functional groups (aldehydes, ketones, acids); dichromate oxidizes secondary alcohols to ketones, so ambiguous.
• D: HCN adds to all carbonyls; LiAlH4 reduces aldehydes/ketones/carboxylic acids, so doesn't specify ketone.

Final answer: C