Compound P(C₈H₈O)$\mathrm{P}(\mathrm{C}_8\mathrm{H}_8\mathrm{O})$ 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. NaHCO₃$NaHCO_{3}$. Compounds P and Q, respectively, are :

Core Logic

Step 1: Degree of Unsaturation for C₈H₈O$C_8H_8O$. DU = C + 1 - H/2 = 8 + 1 - 8/2 = 9 - 4 = 5$DU = C + 1 - H/2 = 8 + 1 - 8/2 = 9 - 4 = 5$. This suggests a benzene ring (DU = 4$DU = 4$) plus one double bond (likely a carbonyl group, C=O$C=O$, since it has one oxygen).

Step 2: Reagent tests.

• Gives a red-orange ppt with 2,4-DNP: It is a carbonyl compound (aldehyde or ketone).
• Does not reduce Fehling's reagent: It is a ketone or an aromatic aldehyde (Fehling's does not react with aromatic aldehydes or any ketones). However, given it requires 'drastic oxidation', it is characteristic of a ketone.
• Drastic oxidation gives Q which effervesces with NaHCO₃$NaHCO_3$: Q is a carboxylic acid. Thus, P is a ketone that oxidizes to an aromatic carboxylic acid.

Step 3: Identification. P is Acetophenone (C₆H₅COCH₃$C_6H_5COCH_3$). Under drastic oxidation with chromic acid, the bond between the carbonyl carbon and the methyl group cleaves, forming Benzoic Acid (Q).

Step 1: Final Conclusion

Compound P is Acetophenone, and Compound Q is Benzoic Acid. (Matches structures provided in the second and third source options natively).

Pattern Recognition

Formula C₈H₈O$C_8H_8O$ with positive 2,4-DNP and negative Fehling's is universally Acetophenone. Its drastic oxidation always yields Benzoic Acid, which gives effervescence with baking soda.

Chapter Mix

Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids