Out of `C_(6)H_(5)CH_(2)Cl` and `C_(6)H_(5)CHClC_(6)H_(5)`, which is more easily hydrolysed by aqueous KOH.

Explanation

The compound `C_(6)H_(5)CH_(2)Cl` is a primary aralkyl halide whiel `C_(6)H_(5)CH(Cl)C_(6)H_(5)` is secondary in nature. The hydrolysis of both these compounds with aqueous KOH (polar) is likely to proceed by `S_(N^(1))` mechanism due to following reasons.
(a). The carbocations formed in both the cases as a result of ionisation are resonance stabilised due to the presence of phenyl groups at the `alpha`-position(s).
(b). As water is a polar solvent, it is expected to favour ionisation of the two halogen substituted compounds leading to `S_(N^(1))` mechanism.
The carbocations that are formed as a result of ionisation in the slow steps are shown:
The ease of hydrolysis depends upon the relative stability of the carbocation/s that are formed in two cases. the secondary carbocation is more stable since the positive charge on the carbocation is delocalised on two phenyl groups that are present at the `alpha`-positions. on the other hand, there is only one phenyl group in primary carbocation available for charge delocalisation.
Thus, we may conclude that `C_(6)H_(5)CHClC_(6)H_(5)` is more easily hydrolysed by aqueous KOH as compared to `C_(6)H_(5)CH_(2)Cl`.