(a) When $n=4,$ what are the possible values of $\ell ?$
(b) When $\ell$ is $2,$ what are the possible values of $m_{\ell} ?$
(c) For a 4 s orbital, what are the possible values of $n, \ell$ and $m_{e} ?$
(d) For a 4 forbital, what are the possible values of $n, \ell$ and $m_{e} ?$