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

The maximum number of electrons that can occupy a single orbital is 2. This is based on the Pauli Exclusion Principle, which states that no two electrons in an atom can have the same set of quantum numbers. Since each electron possesses a unique spin (either spin-up or spin-down), only two electrons can occupy the same orbital while maintaining these distinct characteristics. Therefore, an orbital can hold a maximum of two electrons, with one having a spin of +1/2 and the other -1/2. This foundational concept is critical in understanding electron configurations and the arrangement of electrons in atoms across the periodic table.