Pauli's principle states that in an atom there cannot be more than one electron described by the same combination of the 4 quantum numbers. As an orbital is described by a particular combination of the first three quantum numbers (n, l, and ml), each orbital can only accommodate 2 electrons (one of ms = + 1/2 and the other of ms = -1 / 2). Thus the layer K (n = 1), for which there is only one possible combination of n, l, and ml (that is to say an orbital), can accommodate a maximum of 2 electrons.
That is to say, that contains 4 orbitals, can contain a maximum of 8 electrons.
The orbitals are named s (contains 2 electrons max) p (contains 6 electrons max) d (contains 10 electrons max) and f (contains 14 electrons max).
As you get into the orbitals they have an extra "l" number.
The maximum number of electrons that can contain a given electronic layer is 2 n^2.
Let's go back to the question, for n = 5 the corresponding layer is the "O" layer, as well as the lower layers, and they can contain 50 electrons.
For n = 2 the corresponding layer is the layer "L" and the lower layer "K", and they can contain 8 electrons (2 + 6 electrons).
For n = 3 L = 0 it corresponds to the first under layer with 2 electrons.
For n = 3 L = 1 it corresponds to the second 6-electron sub-layer.
For n = 3 d (corresponding to l = 2) the corresponding layer is the layer "M" and it can contain 10 electrons.
For n = 2 s (corresponding to l = 0) it corresponds to 2 electrons
For n = 5 f (corresponding to l = 3) it corresponds to 14 electrons
