A solution contains one or more of the following ions: Hg₂²⁺ , Ba²⁺ , and Fe²⁺ . When you add potassium chloride to the solution, a precipitate forms. The precipitate is filtered off, and you add potassium sulfate to the remaining solution, producing no precipitate. When you add potassium carbonate to the remaining solution, a precipitate forms. Which ions were present in the original solution?