Combining aqueous solutions of bai2 and na2so4 affords a precipitate of baso4. Which ions are spectator ions in the reaction?

I⁻ (aq) and Na⁺ (aq)

Explanation:

We have the chemical reaction:

BaI₂ + Na₂SO₄ → BaSO₄ + 2 NaI

However if you want to determine the spectator ions you need to write the states of compounds:

(aq) - ions dissolved in water

(s) - solid

Ba²⁺ (aq) + 2 I⁻ (aq) + 2 Na⁺ (aq) + SO₄²⁻ (aq) → BaSO₄ (s) + 2 Na⁺ (aq) + 2 I⁻ (aq)

The ions which does not change the state and remains dissolved in the solution are spectator ions. For our chemical reaction we have the following spectator ions:

I⁻ (aq) and Na⁺ (aq)