$A$ sub-shell with $l = 2$ can accommodate how many electrons?

The number of electrons present in all the completely filled subshells having $n=4$ and $s=+\frac{1}{2}$ is . . . . . . . (Where $n=$ principal quantum number and $s=$ spin quantum number)

Aqueous solution of which salt will not contain ions with the electronic configuration $1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6$?

Which of the following rules is violated by the given electronic configuration?

Write the values of $n, l, m_{l}, m_{s}$ for $4f$.

Which set has the same number of unpaired electrons in their ground state?