Question

Gadolinium has a low value of third ionisation enthalpy because of ______.

Options

• high exchange enthalpy

• high electronegativity

• high basic character

• small size

Answer 1

Gadolinium has a low value of third ionisation enthalpy because of high exchange enthalpy.

Explanation:

Gadolinium (Gd) has an electronic configuration [Xe] 4f⁷ 5d¹ 6s². After removing two electrons (from 6s and 5d), it has a half-filled 4f⁷ configuration, which is very stable. Due to this half-filled 4f subshell, it gains extra stability from exchange energy. So, less energy is needed to remove the third electron, making the third ionisation enthalpy low.