Which of the following ions has the electron configuration 2,8,8?

The electron configuration 2,8,8 represents an atom with 18 electrons, which corresponds to the noble gas argon (Ar). To determine which ion has the same electron configuration, we need to look at the number of electrons that each ion has lost or gained compared to the neutral atom. Na+ has lost one electron, which means it now has 10 electrons, with a configuration of 2,8. This is not the same as 2,8,8, so Na+ is not the correct ion. Mg2+ has lost two electrons, which means it now has 10 electrons, with a configuration of 2,8. This is also not the same as 2,8,8, so Mg2+ is not the correct ion. F- has gained one electron, which means it now has 10 electrons, with a configuration of 2,8. This is not the same as 2,8,8, so F- is not the correct ion. Cl- has gained one electron, which means it now has 18 electrons, with a configuration of 2,8,8. Therefore, the correct answer is Cl-.