Question

Which neutral atom is isoelectronic with Cl-??

Answer 1

For an atom or ion to be isoelectronic to another atom or ion, the SAME amount of electrons must be present. The Cl- anion has 18 electrons. S2- also has 18 electrons so it is isoelectronic. The K+ cation has also lost one electron from its original 19, making it isoelectronic with Cl- as well.

Answer 2

And we can see that the potassium ion, K+, has the same electronic configuration as the chloride ion, Cl-, and the same electronic configuration as an atom of argon, Ar. Therefore, Ar, Cl-, and K+ are said to be isoelectronic species.