Answer:
Every principle energy level can have only one s orbital.
Step-by-step explanation:
For many-electron atoms we use the Pauli exclusion principle to determine electron configurations. This principle states that no two electrons in an atom can have the same set of four quantum numbers. If two electrons in an atom should have the same Principal, Angular Momentum and Magnetic quantum numbers' values (that is, these two electrons are in the same atomic orbital), then they must have different values of Electron Spin Quantum Number. In other words, only two electrons may occupy the same atomic orbital, and these electrons must have opposite spins.