The reaction Ba(NO3)2(aq) + Na2SO4(aq) → 2NaNO3(aq) + BaSO4(s) goes to completion because a

Ba(NO₃)₂ + Na₂SO₄ → 2NaNO₃ + BaSO₄ The reaction goes to completion because it has the same amount of elements in the reactants and products.