Final answer:
In the IUPAC nomenclature system, prefixes are used in the names of covalent compounds to indicate the number of each type of atom present in the molecule.
Step-by-step explanation:
According to the International Union of Pure and Applied Chemistry (IUPAC) nomenclature system, the types of compounds that use prefixes in their names are covalent compounds. Covalent compounds involve a nonmetal bonding with another nonmetal, forming molecules based on shared electrons. Since these compounds can have multiple ratios of elements, prefixes such as mono-, di-, tri-, etc., are used to indicate the number of atoms of each element within the molecule. For example, carbon dioxide is composed of one carbon atom and two oxygen atoms. On the other hand, ionic compounds, particularly those involving transition metals, may use Roman numerals to indicate the charge of the metal ion but do not use prefixes.