Question

Please answer this question

Answer 1

Answer:

4S

Explanation:

by applying aufbau's principle

out of the two 4s will fill up first because it has lower energy than 3d

energy is decided by the 'n+l' value,

n+l value for 3d=3+2=5

n+l value for 4s=4+0=4

hence 4s will fill up first