Here's why:

* Ionic compounds are formed by the electrostatic attraction between positively charged ions (cations) and negatively charged ions (anions).

* Calcium (Ca) loses two electrons to form a cation with a +2 charge (Ca²⁺).

* Oxygen (O) gains two electrons to form an anion with a -2 charge (O²⁻).

* These oppositely charged ions come together to form the neutral compound calcium oxide (CaO).

Therefore, CaO itself is not an ion, but it is composed of ions.