The pair of lanthanides in which both elements have high third – ionization energy is:

Electronic configuration of $\begin{array}{l}\begin{array}{cc}\mathrm{Eu}=4{\text{f}}^{7}6{\mathrm{s}}^2& {\mathrm{Eu}}^{2+}=4{\text{f}}^7\end{array}\\ \begin{array}{cc}\mathrm{Yb}=4{\text{f}}^{14}6{\mathrm{s}}^2& {\mathrm{Yb}}^{2+}=4{\text{f}}^{14}\end{array}\end{array}$
Half filled and completely filled f subshells have extra stability and so have high third ionization energy