(i) Transition metals have the ability to adsorb many other substances on their surface and activate them as a result of chemisorption. Transition metals also exhibit a variety of oxidation states, and can change oxidation states relatively easily. This makes transition metals and their compounds good catalysts.

(ii) ${\mathrm{E}}^{\mathrm{o}}$ values are indicative of the stability of the oxidized form of the element. The lower the ${\mathrm{E}}^{\circ }$ value, more stable the oxidized form of the element. ${\mathrm{Mn}}^{2+}$ with a half filled d-subshell $\left({\mathit{d}}^5\right)$ is stable, so $\mathrm{Mn}$ is easily oxidized to ${\mathrm{Mn}}^{2+}$, making the ${\mathrm{E}}^{\mathrm{o}}$ value negative. ${\mathrm{Cu}}^{2+}$ with a partially filled d subshell $\left({\mathit{d}}^9\right)$ is not stable, and is relatively easily reduced to element form. This makes its ${\mathrm{E}}^{\circ }$ value positive.

(iii) The electronic configurations of actinoids show irregularities because the energies of their $5\mathit{f},6\mathit{d}$, and $7\mathit{s}$-orbitals are close to each other. Electrons can easily move between these subshells.