Identify the major product (P) formed in the given reaction.

The given reaction uses Zn-Hg and conc. HCl, which are the reagents for Clemmensen reduction.

Clemmensen reduction reduces aldehydes and ketones to their corresponding alkanes by converting the carbonyl group ($>C=O$) into a methylene group ($-CH_2-$). The aromatic benzene ring remains unaffected.

In the given reactant:
- The acetyl group ($-COCH_3$) is a ketone and gets reduced to an ethyl group ($-CH_2CH_3$).
- The terminal aldehyde group in $-CH_2CH_2CHO$ gets reduced to a methyl group, converting the entire chain into a propyl group ($-CH_2CH_2CH_3$).

Thus, the major product (P) is 1-ethyl-4-propylbenzene.

Answer: 1-ethyl-4-propylbenzene