JEE Main 2025 Jan 22 Shift 2, Chemistry Q13: Resonance & Mesomeric Effect

The stability of a benzyl cation increases when the substituent on the ring can donate electron density into the ring and, through resonance, into the empty $p$-orbital of the cationic centre.

$-OMe$ is a strong $+M$ (resonance donor) group. At the para position, its lone pair on oxygen can be delocalised into the ring and onto the benzyl carbon, generating an additional resonance structure that places the positive charge on oxygen ($C{H}_3{O}^{+}=...$), strongly stabilising the cation.

$-C{H}_3$ stabilises only weakly via hyperconjugation and $+I$ effect.

At the ortho position, $-OMe$ can also donate by resonance but steric crowding and unfavourable proximity slightly diminish its effect compared with para.

Stability order: para $-OMe$ $>$ ortho $-OMe$ $>$ para $-C{H}_3$ $>$ unsubstituted benzyl.

$\therefore$ Option (1), the $p$-methoxybenzyl cation, is most stable.