The \( f \) orbitals are half and completely filled, respectively in lanthanide ions[Given : Atomic no. Eu, \( 63 \); Sm, \( 62 \); Tm, \( 69 \); Tb, \( 65 \); Yb, \( 70 \); Dy, \( 66 \)]
\( \mathrm{Eu}^{2+} \) and \( \mathrm{Tm}^{2+} \)
\( \mathrm{Sm}^{2+} \) and \( \mathrm{Tm}^{3+} \)
\( \mathrm{Tb}^{4+} \) and \( \mathrm{Yb}^{2+} \)
\( \mathrm{Dy}^{3+} \) and \( \mathrm{Yb}^{3+} \)
