Question

Question #55ae4

Answer 1

3d is higher than 4s

Explanation:

There is not much difference in energy, but 3d is higher than 4s. The relative levels of the different orbitals are shown in the diagram below.

https://en.m.wikipedia.org/wiki/Atom

Therefore, the filling of the 3d orbitals doesn't occur until the 4s orbitals have been filled.