In a reaction involving two ionic compounds where cations and anions swap places, what type of reaction is taking place?

The correct choice is double replacement reaction because in this type of reaction, two ionic compounds exchange their cations and anions to form two new compounds. This typically occurs in aqueous solutions where the ions can freely swap places in the reaction.

For example, consider a reaction between silver nitrate (AgNO3) and sodium chloride (NaCl). The cation from one compound, silver (Ag+), can replace the cation from the other compound, sodium (Na+), leading to the formation of silver chloride (AgCl) and sodium nitrate (NaNO3). This swapping illustrates the fundamental characteristic of a double replacement reaction.

In contrast, a single-replacement reaction involves one element being displaced from a compound by another element. A combination reaction typically involves two or more substances combining to form a single product, while a decomposition reaction involves a single compound breaking down into two or more simpler substances. These differences underscore why the reaction involving the exchange of ions in the question is specifically categorized as a double replacement reaction.