Chemistry - f-block Question with Solution | TestHub

Europium has an atomic number of $63$ and a stable electronic configuration of $\left[\mathrm{Xe}\right]4{\mathrm{f}}^{7}6{\mathrm{s}}^2$. 

Ytterbium, on the other hand, has an atomic number of $70$ and a stable electronic configuration of $\left[\mathrm{Xe}\right]4{\mathrm{f}}^{14}6{\mathrm{s}}^2$. 

Both have high $3^{\mathrm{rd}}$ ionisation energy due to half filled & fully filled configuration respectively.