(i) Transition metals easily form alloys with other transition metals because they have almost similar size. So they can easily replace each other in the crystal lattice.
(ii) The transition metal oxides in the lower oxidation state of metals are basic in nature and in higher oxidation state they are acidic in nature. The oxidation state of $\mathrm{Mn}$ in ${\mathrm{Mn}}_2{\mathrm{O}}_3$ is +3 and ${\mathrm{Mn}}_2{\mathrm{O}}_7$ has +7. Therefore, ${\mathrm{Mn}}_2{\mathrm{O}}_3$ is basic and ${\mathrm{Mn}}_2{\mathrm{O}}_7$ is acidic.
(iii) The common oxidation state of lanthanide metals is $+3.{\mathrm{Eu}}^{2+}$ is formed by losing the two $\mathrm{}\mathit{s}$ electrons, acquires half filled $\left(4{\mathrm{f}}^7\right)$ configuration. But still, they oxidize to their common +3 state. So, the ${\mathrm{Eu}}^{2+}$ loses one electron and is oxidized to ${\mathrm{Eu}}^{3+}$. So ${\mathrm{Eu}}^{2+}$ acts as a strong reducing agent.