Base hydrolysis of $\left[\mathrm{CoCl}\left(\mathrm{NH}_{3}\right)_{5}\right]^{2+}$ is an overall second order reaction, whereas that of $[\mathrm{Co}(\mathrm{CN})]^{3-}$ is of first order. The rates depend in both cases solely on the concentrations of the cobalt complex. This may be due to
\[ \begin{array}{l} \text{(A) Presence of ionizable proton in } \left[\mathrm{CoCl}\left(\mathrm{NH}_{3}\right)_{5}\right]^{2+} \text{ but not in } \left[\mathrm{Co}(\mathrm{CN})_{6}\right]^{3-}, \\ \text{(B) } \mathrm{SN}^{1}{ }_{\mathrm{CB}} \text{ mechanism in the case of } \left[\mathrm{CoCl}\left(\mathrm{NH}_{3}\right)_{5}\right]^{2+} \text{ only} \\ \text{(C) } \mathrm{SN}^{1}{ }_{\mathrm{CB}} \text{ mechanism in the case of } \left[\mathrm{Co}(\mathrm{CN})_{6}\right]^{3-}, \text{ only} \\ \text{(D) } \mathrm{SN}^{1}{ }_{\mathrm{CB}} \text{ mechanism in both the complexes} \end{array} \]