Maximum number of electrons in a subshell with $l = 3$ and $n = 4$ is

Which of the following sets of species has the $3^{rd}$ principal energy level $(n=3)$ completely filled?

Identify the correct statement.

The electronic configuration of $Sc$ $(Z = 21)$ is:

Which of the following is/are not correct with respect to energy of atomic orbitals of hydrogen atom?
$A$. $1s < 2p < 3d < 4s$
$B$. $1s < 2s = 2p < 3s = 3p$
$C$. $1s < 2s < 2p < 3s < 3p$
$D$. $1s < 2s < 4s < 3d$
Choose the correct answer from the options given below:

What is meant by electronic configuration?