Which reagent will distinguish Benzophenone from acetone?

The correct answer is Option (4) → $I_2/NaOH$

Benzophenone is an aromatic ketone, while acetone is a methyl ketone. The distinguishing feature is the presence of the –CO–CH₃ (methyl ketone) group in acetone.

Option 1: Fehling’s reagent Fehling’s solution oxidizes aldehydes to carboxylates giving a brick-red precipitate of Cu₂O. Both benzophenone and acetone are ketones and do not reduce Fehling’s solution. So both give a negative test.

Option 2: Tollen’s reagent Tollen’s reagent gives a silver mirror with aldehydes. Both benzophenone and acetone are ketones and do not react. Hence, this test cannot distinguish them.

Option 3: 2,4-DNP reagent 2,4-DNP reacts with carbonyl compounds (aldehydes and ketones) forming orange precipitates. Both compounds contain a carbonyl group, so both give a positive test. No distinction.

Option 4: I₂ / NaOH (Iodoform test) This test is given by compounds containing a methyl ketone group (–COCH₃). Acetone gives a yellow precipitate of iodoform (CHI₃). Benzophenone lacks this group, so it does not react. This test clearly distinguishes them.