What is the maximum number of electrons that can occupy a single s orbital?

• A. 1 electron
• B. 2 electrons
• C. 6 electrons
• D. 14 electrons

Answer: (B)

Electrons in an orbital are limited by the Pauli exclusion principle and by available spin states. In any given orbital there are two possible spin orientations, up and down. Only one electron with a given spin can occupy the same orbital, so you can place at most two electrons in that orbital, pairing their spins. An s orbital is a single, spherically symmetric region, so it doesn’t add more spin possibilities beyond those two. That’s why the maximum number is two. Numbers like one would leave one spin state unused, while six or fourteen would require more orbitals than a single s orbital provides.