Question

Which one of the following (a or b) electronic configuration is more stable and why?
(a) $3d^{4}4s^2$ (b) $3d^{5}4s^1$

Answer 1

Second electronic configuration is more stable than the first one. This is because it is half filled and thus symmetrical.

When orbitals are half-filled or fully filled, then the electronic configuration becomes more stable.

Accordning half-filled electronic configuration.

$3d^{5}4s^1$ is more stable then $3d^{4}4s^2$.