Silver Mirror test is given by which one of the following compounds?

Tollens’ reagent (ammoniacal $$Ag_2O$$) oxidises aldehydes to salts of carboxylic acids and itself gets reduced to metallic silver, depositing a shining “silver mirror” on the walls of the test-tube.
The test is therefore called the Silver Mirror test.

Key fact: Aldehyde group $$-CHO$$ is required. Simple ketones (both aliphatic and aromatic) do not possess the necessary $$\ce{-CHO}$$ group and hence do not reduce Tollens’ reagent.

Testing the given compounds

• Acetone: $$CH_3COCH_3$$ is a methyl ketone. Ketones generally resist oxidation by Tollens’ reagent → no silver mirror.

• Formaldehyde: $$HCHO$$ is the simplest aldehyde. It readily reduces Tollens’ reagent, producing a bright silver mirror.

• Benzophenone: $$C_6H_5COC_6H_5$$ is an aromatic ketone. Like other ketones, it does not react with Tollens’ reagent.

Hence only formaldehyde gives the Silver Mirror test.

Final answer: Option B which is: Formaldehyde