Aprincipal quantum number refers to

A principal quantum number refers to the energy level of the orbital.

Explanation:

A principal quantum number refers to the energy level of the orbital, the first level being the one with the lowest energy. This orbital refers to the average distance of the electron to the nucleus, this mean when the principal quantum number increases the energy of that orbital increases too but the probability of finding the electron near the nucleus decreases.

This quantum number can take  positive integers from 1 to 7

10 years is the answer