Compound $P$ (\ce{C8H8O}) gives a red-orange precipitate with 2,4-DNP reagent and does not reduce Fehling's reagent. On drastic oxidation with chromic acid, $P$ gives an aromatic product $Q$ that produces effervescence on treatment with aq. \ce{NaHCO3}. Compounds $P$ and $Q$ respectively are:

Solution & Explanation

\textbf{Answer:} (D) \ce{P = C6H5COCH3} (acetophenone); \ce{Q = C6H5COOH} (benzoic acid) \textbf{Solution:} The degree of unsaturation of \ce{C8H8O} is 5: a benzene ring (4) plus one \ce{C=O}. A positive 2,4-DNP test indicates a carbonyl group, and failure to reduce Fehling's rules out an aldehyde, so $P$ is a ketone. The only aromatic \ce{C8H8O} ketone is acetophenone \ce{C6H5COCH3}. On drastic oxidation with chromic acid the entire \ce{-COCH3} side chain is degraded to a single \ce{-COOH} on the ring, giving benzoic acid \ce{C6H5COOH}, which liberates \ce{CO2} with \ce{NaHCO3}: \ce{C6H5COOH + NaHCO3 -> C6H5COONa + H2O + CO2}.