Which of the following reactions is a double substitution reaction?

A double substitution reaction, also known as a double displacement or metathesis reaction, involves the exchange of ions between two compounds to form two new compounds. In this type of reaction, the ions from one reactant switch places with the ions from another reactant, typically resulting in the formation of a precipitate, gas, or water.

In the reaction presented, 2KI and Pb(NO3)2 react to form 2KNO3 and PbI2. Here, potassium (K) ions from potassium iodide (KI) exchange places with lead (Pb) ions from lead nitrate (Pb(NO3)2). This leads to the production of potassium nitrate (KNO3), which remains in solution, and lead iodide (PbI2), which precipitates out of the solution. This characteristic exchange of components is what defines the reaction as a double substitution.

The other reactions do not fit this classification. Cu(s) and AgNO3(aq) initially represent a single substitution reaction where copper displaces silver. The reaction with KClO3 involves decomposition rather than an exchange, and the reaction of CaO with H2O is a combination reaction where the two substances combine to form one new product without any ion exchange