Answer:
Addition of some Na₂SO₄ (aq).
Explanation:
2NaHCO₃ (s) + H₂SO₄ (aq) ⇄ Na₂SO₄ (aq) + 2H₂O (l) + 2CO₂ (g)
According to the Le Chatelier's principle, the addition of Na₂SO₄ to the reaction would lead to shift to the direction of the reaction that consumes Na₂SO₄, in order to reestablish equilibrium. Since the reaction that consumes Na₂SO₄ is the reaction that produces H₂SO₄, the concentration of H₂SO₄ would increase.
