Question

Question #f8cff

Answer 1

The `4s` subshell has a lower energy level compared to the `3d` because it is closer to the nucleus.

Explanation:

The `4s` subshell is overlapped by the `3d` subshell so it is closer to the nucleus.

Imagine the nucleus as your body. The `4s` subshell would be your t-shirt, and the 3d subshell would be your shirt. The
3d is further away from your body so it has a higher energy level.

THE key point is:

The further away a subshell is, the more energy the electrons need to have in order to stay within it's region.