Which of the following compounds will undergo $S_{N}1$ reaction with the fastest rate?

The rate of $S_{N}1$ depends on the stability of the carbocation.Ethyl and $n$ -propyl bromides form primary carbocations (Unstable).Benzyl bromide forms a resonance-stabilized benzyl carbocation.2-Methylbenzyl bromide forms a resonance-stabilized benzyl carbocation where the methyl group at the ortho position provides additional stability through the inductive effect ($+I$) and hyperconjugation. This makes the carbocation even more stable than the simple benzyl one, leading to the fastest rate.