The magnetic quantum number for the valence electron of a sodium atom is:

Given,
$(A)$ $n=5, m_l=-1$
$(B)$ $n=3, l=2, m_l=-1, m_s=+\frac{1}{2}$
The maximum number of electron$(s)$ in an atom that can have the quantum numbers as given in $(A)$ and $(B)$ respectively are:

$4s^2$ is the configuration of the outermost orbit of an element. Its atomic number would be $:-$

The set of quantum numbers for the $19^{th}$ electron in chromium $(Cr)$ is:

The electronic configuration of $Sc$ $(Z = 21)$ is:

Write the electronic configuration of the following ions:
$(a) H^-$
$(b) Na^+$
$(c) O^{2-}$
$(d) F^-$