A principal quantum number refers to: the maximum number of electrons at a given level the total energy of an electron the numbered energy levels starting from the nucleus outward

The principal quantum number refers to the numbered energy levels starting from the nucleus outward. It is denoted by the symbol \( n \) and indicates the relative size and energy of atomic orbitals. The principal quantum number determines the main energy level or shell in which an electron resides, with higher values of \( n \) corresponding to orbitals that are farther from the nucleus and have higher energy.