The electronic configurations of bivalent europium and trivalent cerium are : (atomic number : \( \mathrm{Xe}=54, \mathr…

\( [\mathrm{Xe}] 4 \mathrm{f}^{4} \) and \( [\mathrm{Xe}] 4 \mathrm{f}^{9} \)

\( [\mathrm{Xe}] 4 \mathrm{f}^{7} \) and \( [\mathrm{Xe}] 4 \mathrm{f}^{1} \)

\( [\mathrm{Xe}] 4 \mathrm{f}^{7} 6 \mathrm{~s}^{2} \) and \( [\mathrm{Xe}] 4 \mathrm{f}^{2} 6 \mathrm{s}^{2} \)

\( [\mathrm{Xe}] 4 \mathrm{f}^{2} \) and \( [\mathrm{Xe}] 4 \mathrm{f}^{7} \)