The two electrons in the $K$ shell will differ in which of the following quantum numbers?

The electronic configuration of $Cu$ is

Correct statements for an element with atomic number $9$ are:
$A.$ There can be $5$ electrons for which $m_{s}=+\frac{1}{2}$ and $4$ electrons for which $m_{s}=-\frac{1}{2}$
$B.$ There is only one electron in $p_z$ orbital
$C.$ The last electron goes to an orbital with $n=2$ and $l=1$
$D.$ The sum of angular nodes of all the atomic orbitals is $1$
Choose the correct answer from the options given below:

Write about the subsidiary quantum number $(l)$.

Which of the following elements has the outer electronic configuration $3s^2 3p^5$?

The maximum number of electrons in a subshell of an atom is determined by which of the following expressions?