Why is europium (II) more stable than cerium (II)?

Explanation

Electronic configuration of `Eu^(2+)` is `[Xe] 4 f^(7)5d^(@)` and `Ce^(2+)` is `[Xe]4 f^(1) 5d^(1)` . Since `Eu^(2+)` have half-filled `4 f^(7)` configuration, therefore it is more stable than `Ce^(2+)` in which neither 4 f nor 5d-subshell are half-filled or completely filled.