The fourth period `(n = 4)` does not involve the filling up of electrons in_______subshell.
(i) `4s` (ii) `4p`
(iii) `4d` (iv) `4f`

Options

A. `(iii)`
B. `(iv)`
C. `(iii),(iv)`
D. `(ii),(iii),(iv)`

Answer

C

Explanation

After filling of the `4s` subshell, the filling of the `3d` subshell beings as the energy but higher than that of the `4s`subshell. The filling of `4d` and `4f` subshells does bot occur in this period as their energuies are higher than that of even the `5s` subshell.