Chemistry - f-block Question with Solution | TestHub

In ground state, europium and cerium has following electronic configuration
${\mathrm{}}_{63}\mathrm{E}\mathrm{u}\Rightarrow \left[\mathrm{X}\mathrm{e}\right]4{\mathrm{f}}^{7}6{\mathrm{s}}^2$
${\mathrm{}}_{58}\mathrm{C}\mathrm{e}\Rightarrow [\mathrm{X}\mathrm{e}{]}^4{\mathrm{f}}^{1}5{\mathrm{d}}^{1}6{\mathrm{s}}^2$
Bivalent means Eu lost two electrons and trivalent means Ce lost three electrons so.
$\mathrm{E}{\mathrm{u}}^{2+}\to \left[\mathrm{X}\mathrm{e}\right]4{\mathrm{f}}^7$
$\mathrm{C}{\mathrm{e}}^{3+}:\left[\mathrm{X}\mathrm{e}\right]4{\mathrm{f}}^1$