(a) Because of availability of partially filled orbitals and comparable energies of $ns$ and $(n-1)$ d-orbitals.(b) $E^{\circ}$ value for $\left( \frac{\mathrm{Zn}^{2+}}{\mathrm{Zn}} \right)$ is negative due to stable completely filled $d^{10}$ configuration in $\mathrm{Zn}^{2+}$. The positive value of $\left( \frac{\mathrm{Cu}^{2+}}{\mathrm{Cu}} \right)$ accounts for its ability to liberate $\mathrm{H}_2$ from acids due to its high enthalpy of atomization and low hydration energy.(c) Mn can form multiple bonds with oxygen by using $2p$-orbital of oxygen and $3d$-orbital of $\mathrm{Mn}$ because of which it shows highest oxidation state of +7 with fluorine, Mn cannot form multiple bonds thus shows an oxidation state of +4 .