What are the resulting spectator ions when aqueous solutions of rb2o and cacl2 are added together?

The spectator ions are Rb⁺ and Cl⁻

Explanation:

Spectator ions are the ions that do not take part of the reaction and, so, you do not show them in the net ionic equation.

1) Molecular equation:

You must show the phases

Rb₂O (aq) + CaCl₂ (aq) - -> CaO (s) + 2RbCl (aq)

You are told both Rb₂O and CaCl₂ are in aqueous solutions, so you know their phases and you can write their ionization equations.

2) Ionization

Rb₂O (aq) → 2Rb⁺ + O⁻, and

CaCl₂ (aq) → Ca²⁺ + 2Cl⁻

CaO: as per solubility rules most oxides are usually insoluble. CaO, is slightly soluble. Then, for this exercise you can consider that most CaO is a precipitate (solid phase)

RbCl: as per solubility rules msot chlorides are soluble and RbCl is not an exception, so you get:

RbCl (aq) → Rb⁺ (aq) + Cl⁻ (aq)

3) Total ionic equation:

Now you can write the ionic equation:

2Rb⁺ (aq) + O⁻ (aq) + Ca²⁺ (aq) + 2Cl⁻ (aq) → CaO (s) + 2Rb⁺ (aq) + 2Cl⁻ (aq)

4) Net ionic equation:

Cancel the ions that appear in the same form in the reactant and product sides:

O⁻ (aq) + Ca²⁺ (aq) → CaO (s)

So, you canceled 2Rb⁺ and 2Cl⁻ because they are the spectator ions.