The maximum number of orbitals which can be identified with n=4 and ml=0 is
Answer: 4
Solution
For n=4, the allowed subshells are 4s(l=0), 4p(l=1), 4d(l=2), 4f(l=3). In every subshell, ml=0 corresponds to exactly one orbital, regardless of l. So there is exactly one orbital with ml=0 in each of the four subshells, giving 4 orbitals in total.