Question:
The correct electronic configuration and spin-only magnetic moment $(\mathrm{BM})$ of $\mathrm{Gd}^{3+}(\mathrm{Z}=64)$, respectively, are:
Correct Option: , 2
Solution:
Electronic configuration of
${ }_{64} \mathrm{Gd}=[\mathrm{Xe}] 4 f^{7} 5 d^{1} 6 s^{2}$
${ }_{64} \mathrm{Gd}^{3+}=[\mathrm{Xe}] 4 f^{7}$
No. of unpaired electron $=7$
$\mu=\sqrt{n(n+2)} \mathrm{BM}=\sqrt{63}=7.93 \mathrm{BM}$