Question 4
Counting outwards from the nucleus, how are the shells named?
The right answer is the one marked above.
K, L, M, N … — or, equivalently, 1, 2, 3, 4 … They are two names for the same shells, and you will meet both.
The order matters: K is the innermost, nearest the nucleus. I, II, III, IV are the group numbers of the periodic table, which is something else entirely.