Chemistry - f-block Question with Solution | TestHub

A reducing agent is one of the reactants of an oxidation-reduction reaction which reduces the other reactant by giving out electrons to the reactant. If the reducing agent does not pass electrons to other substances in a reaction, then the reduction process cannot occur.

Europium (atomic number $63$) has the electronic configuration $\left[\mathrm{Xe}\right]4{\mathrm{f}}^{7}6{\mathrm{s}}^2$. It loses two electrons from the 6s energy level and attains a highly stable, half-filled $4{\mathrm{f}}^7$ configuration, and hence it readily forms ${\mathrm{Eu}}^{2+}$ion. ${\mathrm{Eu}}^{2+}$ then changes to the common oxidation states of lanthanides $\left(+3\right)$ and forms ${\mathrm{Eu}}^{3+}$, acting as a strong reducing agent.

$\begin{array}{ll}{\mathrm{Eu}}^{+2}\to & {\mathrm{Eu}}^{+3}+1{\mathrm{e}}^{-}\\ \left[\mathrm{Xe}\right]4{\mathrm{f}}^{7}6 {\mathrm{s}}^0& \left[\mathrm{Xe}\right]4{\mathrm{f}}^{6}6 {\mathrm{s}}^0\end{array}$