Question

Which of the following electronic configuration (a or b) is more stable and why?

(a) 3d⁴4s²

(b) 3d⁵ 4s¹

Answer 1

The atoms with either no electron, exactly half-filled or completely filled electron in their subshells, are having stable electronic configuration.

Sub-shell	No. of half-filled electron	No. of full filled electron
s	1	2
p	3	6
d	5	10
f	7	14

Here, 3d⁵ 4s¹ has a half-filled 'd' subshell and ‘s’ subshell so this electronic configuration is more stable.