Mixing which of the following pairs of solutions will result in the formation of a precipitate?

• A. Na2SO4(aq) and BaCl2(aq)
• B. LiBr(aq) and AgNO3(aq)
• C. NH4Cl(aq) and Na2CO3(aq)
• D. KNO3(aq) and NaCl(aq)

Answer: (A)

Verified step by step guidance

1. Identify the ions present in each solution pair. For example, in Na2SO4(aq) and BaCl2(aq), the ions are Na\textsuperscript{+}, SO4\textsuperscript{2-}, Ba\textsuperscript{2+}, and Cl\textsuperscript{-}.
2. Write the possible combinations of cations and anions that can form when the two solutions are mixed. For Na2SO4 and BaCl2, possible products are BaSO4, NaCl, NaCl, and BaSO4.
3. Use the solubility rules to determine which of these possible products is insoluble in water and will form a precipitate. For example, BaSO4 is known to be insoluble and will precipitate.
4. Repeat this process for each pair of solutions by identifying ions, possible products, and checking their solubility to see if a precipitate forms.
5. Conclude which pairs form a precipitate based on the presence of an insoluble product according to solubility rules.