What is a shell in the context of atomic structure?

The maximum number of electrons that can be accommodated in the $M$ shell is

Phosphorus has three unpaired electrons according to

What are the electronic configurations of elements with atomic numbers $Z = 117$ and $Z = 120$?

The number of unpaired electrons in $Fe^{3+}$ $(Z = 26)$ is:

Consider the following statements:
$(A)$ The principal quantum number $'n'$ is a positive integer with values of $'n'=1, 2, 3, \dots$.
$(B)$ The azimuthal quantum number $'l'$ for a given $'n'$ (principal quantum number) can have values as $'l'=0, 1, 2, \dots, (n-1)$.
$(C)$ Magnetic orbital quantum number $'m_l'$ for a particular $'l'$ (azimuthal quantum number) has $(2l+1)$ values.
$(D)$ $\pm 1/2$ are the two possible orientations of electron spin.
$(E)$ For $l=5$,there will be a total of $11$ orbitals.
Which of the above statements are correct?