What is the electron configuration for the chloride ion (Cl⁻)?

The chloride ion (Cl⁻) is formed when a neutral chlorine atom gains an electron. Chlorine, with an atomic number of 17, has the electron configuration of [Ne] 3s² 3p⁵ in its neutral state. When it gains one additional electron to become Cl⁻, this electron occupies the 3p subshell.

In its ionized state, the chloride ion has a full outer shell configuration of 3s² 3p⁶. This completed configuration corresponds to the noble gas nearest to chlorine, which is argon, making the chloride ion isoelectronic with argon. A full p subshell, along with a filled s subshell, results in an electron configuration that is stable, as it achieves the octet rule.

Thus, the correct electron configuration for the chloride ion is [Ne] 3s² 3p⁶, reflecting this completion of its valence shell and resulting stability.