Answer:2.18 g.
Explanation:To find the mass of sodium sulfate reacted, we use the balanced chemical equation to know that 1 mole of sodium sulfate reacts with 1 mole of barium sulfate. From the given mass of barium sulfate formed, we calculate the number of moles of barium sulfate. Since the stoichiometry of the reaction is 1:1, the number of moles of sodium sulfate reacted is the same as the number of moles of barium sulfate formed. We then use the molar mass of sodium sulfate to calculate the mass of sodium sulfate reacted. The final answer is 2.18 g.