Question

Gadolinium has a low value of third ionisation enthalpy because of

Answer 1

Gadolinium(Z = 64) has configuration $\left[Xe\right]4f^{7}5d^{1}6s^2$ . If it loses $3$ electrons, it will get extra stable half filled 4f subshell, with $4f^7$ configuration which has high exchange energy.