(1) How many subshells are associated with n=4?
(2) How many electrons will be present in the subshells having `m_(s)` value of `-(1)/(2)` for n=4?

Explanation

(1) For n=4, l=0,1,2,3. Thus, the energy level with n=4 contains four subshell (4s, 4p,4d and 4f).
(2) For n=4, number of orbitals `(n)^(2)=(4)^(2)=16`. Each orbital will have only one electron with `m_(s)=-(1)/(2)`. Hence, for n=4,16 electrons will be present in the subshells withh the value of `m_(s)=-(1)/(2)`.