Mention the sequence in which the following orbitals are filled up by electrons: 3d and 4p.

Explanation

The energy of a given subshell is determined by the algebraic sum of 'n' and 'l' i.e., n+l. if the 'n+l' values of any two subshells are equal, then the electron enters the one with lower 'n'.
In the 3d-subshell, n=3, l=2, `thereforen+l=3+2=5`
In the 4p-subshell, n=4, l=1 `therefore n+l=4+1=5`
Since for 3d-subshell, n=3 which is lower than that of 4p where n=4, electrons first enters the 3d-subshell.