An argon atom is isoelectronic with what?

Answer 1

Neutral argon (Ar) is isoelectronic (has the same number of electrons) as:

Cl-
S-2
P-3
K+
Ca+2

Answer 2

Isoelectroni means having the same number of electrons. Since every atom has unique number of electrons, no two atoms are isoelectroni unless they are isotopes. But, ions can be isoelectronic with atoms. I'll give a list of some ionsisoelectronic with argon:
1. K+
2. Ca2+ or Ca+2
3. Sc 3+ or Sc +3
4. Cl-
5. S2- or Sc -2
6. P3- or P-3