Compound \(P \left( C _8 H _8 O \right)\) gives a red orange precipitate with 2, 4-DNP reagent and it does not reduce Fehling's reagent. On drastic oxidation with chromic acid, \(P\) gives an aromatic product \(Q\) that produces effervescence on treating with aq. \(NaHCO _3\). Compounds P and Q , respectively, are :

(D) 4
Compound \(P \left( C _8 H _8 O \right)\) gives a red-orange precipitate with 2,4 -DNP reagent, indicating the presence of a carbonyl group.
P does not reduce Fehling's reagent, which implies it is either a ketone or an aromatic aldehyde.
The requirement of "drastic oxidation" strongly suggests that P is a ketone. Ketones resist mild oxidation and require drastic conditions (such as chromic acid) to undergo C-C bond cleavage, whereas aldehydes are easily oxidized.
Acetophenone \(\left( C _6 H _5 COCH _3\right)\) is a ketone that fits the molecular formula \(C _8 H _8 O\).
Drastic oxidation of acetophenone with chromic acid cleaves the methyl group to yield benzoic acid ( \(C _6 H _5 COOH\) ), which is compound Q .
Benzoic acid is an aromatic carboxylic acid that reacts with aqueous \(NaHCO _3\) to produce effervescence of \(CO _2\) gas.
Therefore, P is acetophenone and Q is benzoic acid.