JEE Main · 2026 · 28 Jan 2026 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

The four isomers are 1-phenylprop-2-en-1-ol (P, an allylic alcohol carrying a $\mathrm{C}=\mathrm{C}$), 3-phenylpropanal (Q, an aldehyde), 1-phenylpropan-2-one (R, a methyl ketone) and 1-phenylpropan-1-one (S, propiophenone). Q, R and S each hold a carbonyl group and so give the 2,4-DNP precipitate, while P does not. Q and R are aromatic and burn with a sooty flame. Only Q is an aldehyde, so only Q reduces Tollens\textquoteright{} reagent to deposit silver. Baeyer\textquoteright s test needs the $\mathrm{C}=\mathrm{C}$ that only P has, so the pairing of P with Q is not correct; the iodoform test needs a $\mathrm{CH}{}_3\mathrm{CO}{}^{-}$ group, which only R has (S is $\mathrm{Ph}-\mathrm{CO}-\mathrm{CH}{}_2\mathrm{CH}{}_3$), so the pairing of R with S is not correct. The correct statements are that Q, R and S give the 2,4-DNP test, that Q and R give a sooty flame, and that Q alone answers Tollens\textquoteright{} reagent.