For a given value of ‘n’, ‘l’ can have values from zero to (n – 1).
Four sub-shells are associated with n = 4, which are s, p, d and f.
b) For n=4
the no of orbitals will be(n^2) that is 16
2 electrons will go to each orbital with spins -1/2 and +1/2
therefore no of electrons having spin -1/2 will be 16