(A) ‌58Ce⟶[Xe]4f25d06s2 In complex Ce+4⟶[Xe]4f05d06s0 There is no unpaired electron, so µm=0BM (B) ‌64Gd⟶[Xe]4f75d16s2 In complex, ‌64Gd2+⟶[Xe]4f75d1 There are 8 unpaired electrons. ∴‌‌µm=√8(8+2)=√80=8.94BM (C) ‌63Eu⟶[Xe]4f95d06s0 In complex ‌63Eu+3⟶[Xe]4f65d06s0 contain six unpaired electrons. So, µm=√6(6+2)=√48BM=6.93BM Hence, order of spin only magnetic moment B>C>A