Q. The +3 ion of which one of the following has half-filled $4f$ sunshell?
A) La
B) Lu
C) Gd
D) Ce
Explanation
(c)
$Gd = \lbrack Xe\rbrack 4f^{7}5d^{1}6s^{2}$,
$Gd^{3 +} = \lbrack Xe\rbrack 4f^{7}$ (half-filled)
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.