(a) How many sub-shells are associated wit n = 4 ? (b) How many electrons will be present in the sub-shell having `m_s` value of `1//2` for `n = 4` ?

Explanation

Sub-shell in `n = 4` are 4 i.e., 4s , 4p , 4d and 4f .
No. of electrons having `m_s = -1//2` for `n = 4` will be 16.