Concept:This statement describes the order in which electrons fill atomic orbitals.Explanation:According to the Aufbau Principle, electrons first occupy the lowest available energy levels before moving to higher ones.This matches exactly the given statement: "Electrons always occupy the lowest empty energy level."Hund's rule deals with degenerate orbital filling, and the Pauli Exclusion Principle deals with electron spin pairing, so they are not correct here.Answer:A. Aufbau Principle