Final answer:
A salt is formed when a reaction between an acid and a base replaces the acid's hydrogen with a cation.
Step-by-step explanation:
When an acid reacts with a base, the acid's hydrogen is replaced by a cation, resulting in the formation of a salt. A salt is an ionic compound made by combining an acid with a base. Therefore, the compound formed when a reaction between an acid and a base replaces the acid's hydrogen with a cation is a salt.