Halide most readily hydrolyses is $\left({\mathrm{SN}}_1\right)$

The carbocation ${\left({\mathrm{C}}_6{\mathrm{H}}_5\right)}_3{\mathrm{C}}^{+}$ which is obtained during $\left({\mathrm{SN}}_1\right)$ reaction of ${\left({\mathrm{C}}_6{\mathrm{H}}_5\right)}_3\mathrm{CCl}$ is stabilizes by resonance with three phenyl groups. Hence, it is most stable and easily formed.

Due to this reason, ${\left({\mathrm{C}}_6{\mathrm{H}}_5\right)}_3\mathrm{CCl}$ is most readily hydrolyzed by ${\mathrm{SN}}_1$ mechanism.