Final answer:
Double-replacement reactions often involve the exchange of cations and anions between two compounds, which can result in the formation of a gas, a precipitate, or a weak electrolyte.
Step-by-step explanation:
The initial question seems to combine elements from multiple problems but is asking for the products of a double-replacement reaction.
For example, in the reaction Na₂S + 2HCl → 2NaCl + H₂S, sodium sulfide and hydrochloric acid mix to produce aqueous sodium chloride and hydrogen sulfide gas, which is a typical formation of a gas during a double-replacement reaction. Another instance is the double-replacement reaction NaCN + HBr → NaBr + HCN, where hydrogen cyanide gas is formed.
Double-replacement reactions generally involve two compounds where the cations and anions exchange partners to form two new compounds, typically producing a gas, a precipitate, or a weak electrolyte (like water).