Which neutral atom is isoelectronic with Cl-??

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.

Density and pressure