The orbital angular momentum of an electron in $2s$ orbitals is

In a multi-electron atom,which of the following orbitals described by the three quantum numbers will have the same energy in the absence of magnetic and electric fields?
$1. n = 1, l = 0, m = 0$
$2. n = 2, l = 0, m = 0$
$3. n = 2, l = 1, m = 1$
$4. n = 3, l = 2, m = 0$
$5. n = 3, l = 2, m = 0$

Find the number of electron pairs in $P$ atom with $l = 1$ and $m = 0$.

The magnetic quantum number for the valence electron of sodium is

Statement $A$: An orbital can accommodate a maximum of two electrons.
Reason $R$: Two electrons in an orbital produce opposite magnetic fields.

Number of unpaired electrons in the ground state of beryllium atom is