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

Each orbital can hold a maximum of two electrons. 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. In practical terms, this means that within a specific orbital, one electron may have a spin-up orientation, while the other must have a spin-down orientation. Hence, the orbital can accommodate a pair of electrons with opposite spins.

In contrast, while the number 1 represents a situation where only one electron is present in an orbital, it does not take into account the capacity of that orbital to hold a second electron. The number 8 refers to the total number of electrons that can fill a shell (as described by the formula 2n², where n represents the principal quantum number) but is not relevant to the specific capacity of an individual orbital. The formula for the maximum number of electrons in a shell does not apply directly to individual orbitals.