What happens during a single substitution reaction?

In a single substitution reaction, one element displaces another element within a compound. This reaction involves a single compound and a free element, where the free element replaces one of the elements in the compound. For instance, if you have a reaction involving zinc and hydrochloric acid, zinc can replace the hydrogen in hydrochloric acid, leading to the formation of zinc chloride and hydrogen gas. This type of reaction is significant in various fields such as chemistry and materials science, as it illustrates how elements can interact and change their bonding depending on their reactivity and conditions.

The other options describe different types of chemical reactions. For instance, the combination of two reactants to form a single product represents a combination reaction, while the exchange of ions typically describes a double substitution reaction. The decomposition of a compound into individual elements reflects a decomposition reaction. Each of these reactions has distinct characteristics and mechanisms that set them apart from a single substitution reaction.