Final answer:
A precipitate was formed when AgNO3 and NaCl reacted in aqueous solution, leading to the formation of insoluble AgCl, explained by a double-replacement reaction. Therefore correct option is D
Step-by-step explanation:
When a student mixed aqueous solutions of AgNO₃ (silver nitrate) and NaCl (sodium chloride), a white, powdery substance settled out of the solution. This observation can be explained by the fact that a precipitate was formed. In this case, a double-replacement reaction occurred where Ag (silver) ions from AgNO₃ and Cl (chloride) ions from NaCl exchanged partners, leading to the formation of AgCl (silver chloride), which is insoluble in water and thus precipitated out of the solution. The balanced chemical equation representing this reaction is AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq). The correct statement that explains what happened is D. A precipitate was formed.