Carbonyl X is a symmetrical ketone that forms an achiral cyanohydrin and fails Fehling's test.

Steps:

• Carbonyl compounds react with HCN/NaCN to form cyanohydrins; aldehydes and ketones both do this.
• Fehling's reagent tests positive only for aldehydes (oxidizable to carboxylic acids), not ketones.
• X does not react with Fehling's, so X is a ketone (eliminate A and C, both aldehydes).
• Among ketones, propanone (D) forms an achiral cyanohydrin (CH3-C(OH)(CN)-CH3, identical substituents on central carbon), unlike butanone (B, chiral cyanohydrin with CH3 and CH2CH3 groups).

Why D is correct:

• Propanone is a symmetrical ketone (CH3COCH3); its cyanohydrin has a plane of symmetry, making it achiral, and ketones do not reduce Fehling's reagent.

Why the others are wrong:

• A. Butanal is an aldehyde; reacts with Fehling's.
• B. Butanone is an unsymmetrical ketone; forms chiral cyanohydrin.
• C. Propanal is an aldehyde; reacts with Fehling's.

Final answer: D