Which rule describes the arrangement of electrons in subshells of the same energy?

For hydrogen-like atoms,the average distance of an electron from the nucleus for the orbitals belonging to the $4^{th}$ orbit is minimum for:

The quantum numbers $n$ and $l$ for four electrons are given as: $(1) \, n = 4, l = 1; \, (2) \, n = 4, l = 0; \, (3) \, n = 3, l = 2; \, (4) \, n = 3, l = 1$. Arrange them in increasing order of their energy.

What is the maximum number of electrons that can be associated with the following set of quantum numbers?
$n = 3, l = 1$ and $m = -1$

What is the lowest value of $n$ that allows $g$ orbitals to exist?

What is a shell in the context of atomic structure?