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

Each orbital in an atom can hold a maximum of two electrons. This is due to the Pauli exclusion principle, which states that no two electrons can have the same set of four quantum numbers within a given quantum system.

In an orbital, electrons must have opposite spins when they occupy the same region of space. This means that one electron will have a spin of +1/2, while the other will have a spin of -1/2, allowing them to coexist in the same orbital without violating the exclusion principle. Thus, the correct answer is that a maximum of two electrons can occupy a single orbital.