Question

The +3 ion of which one of the following has half filled 4f subshell:

• A. $La$
• B. $Lu$
• C. $Gd$
• D. $Ac$

Answer 1

Answer: (C)

$Gd$

Electronic configuration of outer shell in $Gd$ is $4f^{7}5d^{1}6s^2$.
Electronic configuration of outer shell in $G{d}^{+3}$ is $4f^7$.