The mixing of barium chloride and sodium sulfate is a precipitate reaction. This reaction generates barium sulfide and sodium chloride.

In a precipitation reaction, dissolved ionic compounds mix in water and form an insoluble solid. Barium chloride and sodium sulfate are therefore liquids in solution, while the actual precipitate is barium sulfate: BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq). The question says “barium sulfide,” but that is not the product of this reaction; choice D is the intended answer because it identifies the reactants as liquids and a product as solid.

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