The maximum number of electrons which each sub-shell can occupy is

The electrons would go to lower energy levels first and then to higher energy levels according to which of the following?

For a magnetic quantum number $m = 0, \pm 1$,the value of the principal orbital (azimuthal quantum number $l$) corresponds to which subshell,and what is the minimum principal quantum number $n$ required for this set?

The orbital angular momentum of an electron in $3s$ orbital is $\frac{xh}{2\pi}$. The value of $x$ is . . . . . . .

Which one represents an impossible arrangement of quantum numbers $(n, l, m, s)$?

Determine the number of $d$-electrons in $Fe^{2+} (Z = 26)$.