(i) ${\mathrm{Cu}}^{2+}$ salts are coloured whereas ${\mathrm{Zn}}^{2+}$ salts are white because ${\mathrm{Cu}}^{2+}\left(\left[\mathrm{Ar}\right]3{\mathit{d}}^9\right)$ has one unpaired electron in $\mathit{d}$-orbital which allows electron transition in visible region which imparts colour whereas ${\mathrm{Zn}}^{2+}\left(\left[\mathrm{Ar}\right]3{\mathit{d}}^{10}\right)$ do not possess any unpaired electron hence no electron transition takes place thus shows no colour.
(ii) ${\mathrm{E}}^{\circ }$ values for ${\mathrm{Mn}}^{3+}∕{\mathrm{Mn}}^{2+}$ couple is much more positive than for ${\mathrm{Cr}}^{3+}∕{\mathrm{Cr}}^{2+}$ because the conversion of ${\mathrm{Mn}}^{2+}$ from ${\mathrm{Mn}}^{3+}$ possesses extra stability due to half filled valence electronic configuration $\left(3{\mathit{d}}^5\right)$ whereas $\mathrm{Cr}$ ion changes from ${\mathrm{Cr}}^{3+}$ to ${\mathrm{Cr}}^{2+}$ undergoes change in outer configuration from $3{\mathit{d}}^{\mathit{\beta }}$ to $3{\mathit{d}}^4$ making it less stable comparatively.
(iii) Transition metals have very similar atomic sizes as a result one metal can easily replace the other metal from its lattice to form solid solution (alloy). Transition metals are also miscible with one another in the molten state. Thus, the molten state solution of two or more transition metals on cooling forms alloy.