Functional group identification from composition and tests

Steps:

• Calculate empirical formula from mass percentages and Mr=72: C (66.7/12=5.56 mol), H (11/1=11 mol), O (22.2/16=1.39 mol); divide by 1.39 yields C₄H₈O.
• Orange precipitate with 2,4-DNPH indicates carbonyl group (aldehyde or ketone).
• No reaction with Fehling's reagent rules out aldehyde.
• Thus, X contains a carbonyl but is not an aldehyde.

Why A is correct:

• 2,4-DNPH reagent reacts with carbonyl compounds (C=O) to form hydrazones, giving orange precipitate, confirming X has C=O group.

Why the others are wrong:

• B: Acetone (CH₃COCH₃) has Mr=58, not 72.
• C: Butanone fits C₄H₈O and tests, but multiple ketones possible; info does not specify structure.

Final answer: A