Question

fill in the blank question
the number assigned to each orbit of an electron is called a(n) number.

Explanation:

In atomic structure, the principal quantum number ($n$) is used to denote the energy level (or orbit) of an electron. It takes positive integer values ($n = 1,2,3,\cdots$). As $n$ increases, the electron is in a higher - energy orbit that is farther from the nucleus.

Answer:

principal