Question

The electronic configuration of $Eu$ (Atomic $No.63$), $Gd$ (Atomic $No.64$) and $Tb$ (Atomic $No.65$) are :

• A. $[Xe]4f^{7}6s^2,[Xe]4f^{8}6s^2$ and $[Xe]4f^{8}5d^{1}6s^2$
• B. $[Xe]4f^{7}5d^{1}6s^2,[Xe]4f^{7}5d^{1}6s^2$ and $[Xe]4f^{9}6s^2$
• C. $[Xe]4f^{6}5d^{1}6s^2,[Xe]4f^{7}5d^{1}6s^2$ and $[Xe]4f^{8}5d^{1}6s^2$
• D. $[Xe]4f^{7}6s^2,[Xe]4f^{7}5d^{1}6s^2$ and $[Xe]4f^{9}6s^2$

Answer 1

Answer: (D)

The electronic configuration of $Eu$ (Atomic $No.63$), $Gd$ (Atomic $No.64$) and $Tb$ (Atomic $No.65$) are :
$[Xe]4f^{7}6s^2,[Xe]4f^{7}5d^{1}6s^2$ and $[Xe]4f^{9}6s^2$ respectively.
$Gd$ possesses a single electron in the $5d$ subshell. In the case of other lanthanoids, the $5d$ orbital is empty.