6. A solution contains the ions Ag⁺, Pb²⁺, and Ni²⁺. Dilute solutions of NaCl, Na₂SO₄, and Na₂S are available to separate the positive ions from each other. In order to effect separation, the solutions should be added in which order? (A)Na₂SO₄, NaCl, Na₂S (B)Na₂SO₄, Na₂S, NaCl (C)Na₂S, NaCl, Na₂SO₄ (D)NaCl, Na₂S, Na₂SO₄ (E)NaCl, Na₂SO₄, Na₂S