Which prefix would you use to describe four atoms?

The prefix that describes four atoms is "tetra." In the naming conventions used in chemistry, prefixes are attached to the names of compounds or molecules to indicate the number of atoms of a particular element present.

The prefix "tetra" originates from the Greek word for four and is commonly used in both organic and inorganic chemistry. For instance, in chemical nomenclature, a molecule with four hydrogen atoms bonded to a central atom might be referred to as a "tetrahydride." Understanding these prefixes helps in properly identifying and communicating the structure of chemical compounds.

The other prefixes mentioned—hexa, di, and tri—indicate six, two, and three atoms, respectively. Each of these serves a specific purpose in molecular naming but does not convey the same count as "tetra," which is strictly for four.