Which of the following shows half-filled configuration?

$(a)$ How many sub-shells are associated with $n=4?$
$(b)$ How many electrons will be present in the sub-shells having $m_{s}$ value of $-1/2$ for $n=4?$

Consider the following pairs of electrons:
$(A)$ $(a)$ $n=3, l=1, m_{l}=1, m_{s}=+\frac{1}{2}$
$(b)$ $n=3, l=2, m_{l}=1, m_{s}=+\frac{1}{2}$
$(B)$ $(a)$ $n=3, l=2, m_{l}=-2, m_{s}=-\frac{1}{2}$
$(b)$ $n=3, l=2, m_{l}=-1, m_{s}=-\frac{1}{2}$
$(C)$ $(a)$ $n=4, l=2, m_{l}=2, m_{s}=+\frac{1}{2}$
$(b)$ $n=3, l=2, m_{l}=2, m_{s}=+\frac{1}{2}$
The pair$(s)$ of electrons present in degenerate orbitals is/are...... .

The number of quantum numbers required to describe an electron in an atom completely is

The maximum number of electrons present in an orbit with azimuthal quantum number $l = 3$ is:

Which quantum number determines the shape of the subshell?