\(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{Cl}\) is \(1^{\circ}\) aryl halide while \(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}(\mathrm{Cl}) \mathrm{C}_6 \mathrm{H}_5\) is a \(2^{\circ}\) aryl halide. In \(\mathrm{S}_{\mathrm{N}}\) 1 reactions, the reactivity depends upon the stability of carbocations.



Since the \(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CHC}_6 \mathrm{H}_5\) carbocation is more stable than \(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2^{+}\)carbocation, therefore, \(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CHClC}_6 \mathrm{H}_5\) gets hydrolysed more easily than \(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{Cl}\) under \(\mathrm{S}_{\mathrm{N}} 1\) conditions. However, under \(\mathrm{S}_{\mathrm{N}} 2\) conditions, the reactivity depends on steric hindrance, therefore, under \(\mathrm{S}_{\mathrm{N}} 2\) conditions, \(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{Cl}\) gets hydrolysed more easily than \(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CHClC}_6 \mathrm{H}_5\).