Carbonyl compound identification via selective tests

Steps:

• Positive DNPH test indicates a carbonyl group (aldehyde or ketone) in Q, as it forms a hydrazone precipitate.
• Negative Fehling's test means Q lacks reducing properties, ruling out aldehydes but allowing ketones.
• Examine options: A is an alkane (no carbonyl); B and D are aldehydes (CH3CH2CHO); C is a ketone (CH3CH2COCH3).
• Only C fits both tests: carbonyl for DNPH, non-reducing for Fehling's.

Why C is correct:

• CH3CH2COCH3 (butanone) has C=O group reacting with DNPH per hydrazone formation, but as a ketone, it resists oxidation by Cu2+ in Fehling's (aldehydes reduce to carboxylic acids, giving red Cu2O precipitate).

Why the others are wrong:

• A: CH3CH2CH3 (propane) lacks carbonyl, so no DNPH precipitate.
• B: CH3CH2CHO (propanal) is an aldehyde, reacts with both DNPH and Fehling's (positive reducing test).
• D: Identical to B, so same error as B.

Final answer: C