The most stable carbocation from the following is:

Step 1: Analyzing Benzyl Carbocation Stability Substituents on the benzene ring affect stability:

• $\ce{-OCH3}$ at para: Strong $+R$ effect stabilizes the positive charge.
• $\ce{-CH3}$ at para: $+I$ and hyperconjugation stabilize the charge (weaker than $+R$).
• $\ce{-OCH3}$ at meta: Only $-I$ effect (destabilizes the positive charge as $+R$ doesn't reach meta).

Step 2: Conclusion $p$-Methoxy benzyl carbocation is the most stable due to the strong resonance (+R) stabilization by the methoxy group.

$\boxed{\text{Answer: (b) p-Methoxy benzyl carbocation}}$