In naming covalent molecules, which statement is true regarding prefixes?

• A. Only the first element uses prefixes
• B. There are no prefixes in covalent naming
• C. Both elements may use prefixes, with the second element always using a prefix and the first element using a prefix if more than one atom
• D. Prefixes indicate the element's oxidation state

Answer: (C)

In covalent naming, prefixes tell you how many atoms of each element are present in the molecule. The first element gets a prefix only if there’s more than one atom of that element, and the second element also uses a prefix to show its count (though in practice the “mono-” for a single second element is often omitted in simple names). This is why a compound with two nitrogens and five oxygens is named di-nitrogen pentoxide, and carbon monoxide has no prefixes because there is only one atom of each element. Prefixes indicate atom counts, not oxidation state.