Which is the correct term for a substance with two atoms?

The term that describes a substance consisting of two atoms is derived from the prefix "Di-," which comes from the Greek word meaning "two." This prefix is commonly used in chemistry, especially when naming molecules or compounds that have two atoms of the same or different elements. For example, in the molecular formula for oxygen gas (O2), the "di" indicates that there are two oxygen atoms bonded together.

The other prefixes relate to different quantities: "Mono-" means one, "Tri-" means three, and "Tetra-" means four. Therefore, for identifying substances based on the number of atoms, "Di-" is the appropriate and correct term for two-atom substances.