Looking for classes? Ksquare Career Institute, Bengaluru →
Gadolinium has a low value of third ionisation enthalpy because of
A
high basic character
B
small size
C
high exchange enthalpy
D
high electronegativity
Detailed Solution
$_{64}Gd = [Xe]\,4f^7 5d^1 6s^2$; $Gd^{2+} = [Xe]\,4f^7 5d^1$
The third electron is removed from 5d, leaving the stable half-filled $4f^7$ configuration, which has maximum exchange energy.
So Gd has a low third ionisation enthalpy because of high exchange enthalpy.