The $\mathrm{pH}$ of the solutions will be as given below:

$$\begin{gathered} \mathrm{I}. {\mathrm{CuSO}}_4: \text{Salt of strong acid and weak base }\left(\mathrm{pH}<7\right) \\ \mathrm{II}. \mathrm{NaCN}: \text{Salt of weak acid and strong base} \left(\mathrm{pH}>7\right) \\ \mathrm{III}. \mathrm{KCl}:\text{ Salt of strong acid and strong base} \left(\mathrm{pH}=7 \right) \end{gathered}$$