Question

4s orbital is filled prior to 3d orbital

Answer 1

since electrons are filled on the basis of their energy level
and in 4s ,n+l value=4+0=4
and in 3d,n+l value=3+2=5

as you can see the energy of 3d orbital is more than 4s
hence 4s orbital is filled first



hope it helps you :)

Answer 2

Answer:

the 4s orbitals have a lower energy than the 3d, and so the 4s orbitals are filled first. We know that the 4s electrons are lost first during ionization. The electrons lost first will come from the highest energy level, furthest from the influence of the nucleus.