d
\((a)\) \({ }_{58} Ce \rightarrow[ Xe ] 4 f ^{2} 5 d ^{0} 6 s ^{2}\)

In complex \(Ce ^{4+} \rightarrow[ Xe ] 4 f ^{0} 5 d ^{0} 6 s ^{0}\)

there is no unpaired electron so \(\mu_{ m }=0\)

\((b)\) \({ }_{64} Gd ^{3+} \rightarrow[ Xe ] 4 f ^{7} 5 d ^{0} 6 s ^{\circ}\)

contain seven unpaired electrons so, \(\mu_{ m }=\sqrt{7(7+2)}=\sqrt{63} B.M\)

\((c)\) \({ }_{63} Eu ^{3+} \rightarrow\left[{ }_{54} Xe \right] 4 f ^{6} 5 d ^{0} 6 s ^{\circ}\)

contain six unpaired electron

so, \(\mu_{ m }=\sqrt{6(6+2)}=\sqrt{48} B . M\)

Hence, order of spin only magnetic movement

\(b > c > a\)