Integers or half-integers used to identify specific electrons in atoms are called

• A. Electron spins
• B. Quantum numbers
• C. Principal values
• D. Azimuthal numbers

Answer: (B)

Integers or half-integers used to identify specific electrons in atoms are called quantum numbers. They form a four-number label for each electron that encodes its energy level, subshell shape, orbital orientation, and spin: the principal quantum number n (a positive integer) sets the energy level, the azimuthal quantum number l (0 to n−1) defines the subshell type, the magnetic quantum number m_l (ranging from −l to +l) specifies the orbital orientation, and the spin quantum number m_s (±1/2) gives the electron’s spin. Because these values include both integers and half-integers, they uniquely identify every electron in an atom, and the Pauli exclusion principle requires that no two electrons share all four quantum numbers. The other terms refer to only part of this labeling or describe a single aspect (like spin), so they don’t provide the complete identifier for an electron.