Chemistry - f-block Question with Solution | TestHub

An oxidizing agent itself gets reduced. ${\mathrm{Tb}}^{4+}$ has an electronic configuration of $[\mathrm{Xe}]4f^7$. It readily gains an electron to form ${\mathrm{Tb}}^{3+}$ ($[\mathrm{Xe}]4f^8$), which is more stable due to the half-filled $f$-subshell in ${\mathrm{Tb}}^{4+}$ becoming $4f^8$ in ${\mathrm{Tb}}^{3+}$. This tendency to gain an electron makes ${\mathrm{Tb}}^{4+}$ a good oxidizing agent.