For azimuthal quantum number $l = 3$,the maximum number of electrons will be

Which set of quantum numbers is correct for the valence electron of $Na$?

Arrange the following orbitals in decreasing order of energy:
$A$. $n = 3, l = 0, m = 0$
$B$. $n = 4, l = 0, m = 0$
$C$. $n = 3, l = 1, m = 0$
$D$. $n = 3, l = 2, m = 1$
The correct option for the order is:

Which of these species will have a non-zero magnetic moment?

Number of nodal centres (radial nodes) for $2s$ orbital is:

While filling up of electrons in the atomic orbitals,the $4s$ orbital is filled before the $3d$ orbital,but the reverse happens during the ionization of the atom. Explain why?