2,4-DNPH Test for Aldehydes and Ketones Steps:

• Recall that 2,4-dinitrophenylhydrazine (DNPH) reacts with carbonyl groups (C=O) in aldehydes and ketones to form yellow-orange hydrazone precipitates.
• Examine each choice for the presence of an aldehyde (-CHO) or ketone (>C=O) functional group.
• Eliminate options lacking a reactive carbonyl, such as alcohols, carboxylic acids, or esters.
• Identify the option with an aldehyde or ketone as the positive result.

Why D is correct:

• Compound D contains a ketone group, which reacts with DNPH to form the characteristic yellow-orange 2,4-dinitrophenylhydrazone precipitate, as per the standard carbonyl identification test.

Why the others are wrong:

• A lacks a carbonyl; it's an alcohol that does not react with DNPH.
• B is a carboxylic acid; the -COOH group does not form a precipitate with DNPH.
• C is an ester; esters are unreactive toward DNPH under test conditions.

Final answer: D