Question

The lanthanides have electron configuration with $6s^2$ in common but with variable occupation of the:

• A. 6 p-level
• B. 5 p-level
• C. 5 d-level
• D. 4 f-level

Answer 1

Answer: (D)

4 f-level

lanthanide atoms have configurations of the type $\left[Xe\right]4f^{1-14}6s^2$.
So here 4f level have variable occupation.