A chloride ion (Cl-) has the same number of electrons as a neutral argon (Ar) atom.

Here's why:

* Chlorine (Cl) has 17 protons and 17 electrons in its neutral state.

* A chloride ion (Cl-) gains one electron, bringing its total to 18 electrons.

* Argon (Ar) is a noble gas with 18 protons and 18 electrons.

Therefore, a chloride ion has the same electron configuration as a neutral argon atom.