A Level Chemistry OCR Practice Exam

An atomic orbital can hold up to two electrons, and crucially, these electrons must have opposite spins. This principle is rooted in the Pauli Exclusion Principle, which states that no two electrons in an atom can have the same set of quantum numbers. Since one of the quantum numbers defines the spin of the electron, having two electrons in the same orbital means they must have opposite spins—one with spin-up and the other with spin-down.

The concept of orbitals is fundamental to understanding electron configuration in atoms. Each orbital can be thought of as a region in space where there is a high probability of finding an electron. The restriction to two electrons per orbital, with the requirement for opposite spins, ensures that electrons can occupy the same orbital without violating quantum mechanical rules.

In contrast, the other options suggest conditions that either exceed the capacity of a single orbital or do not align with how electrons are structured in an atom.