An example of which type of element is oxygen, which exists as O2?

Oxygen, in its molecular form as O2, is classified as a diatomic element. This designation means that it consists of two atoms of the same element bonded together. Diatomic elements are those that naturally occur as molecules made up of two identical atoms.

In contrast, a monatomic element consists of single atoms that are not bonded to other atoms. Examples include noble gases such as helium or neon, which exist independently and do not form bonds to create diatomic or polyatomic structures.

Polyatomic elements, on the other hand, are formed by combinations of three or more atoms, which can be the same element (like phosphorus tetramers) or different elements. An example of polyatomic oxygen molecules would be ozone (O3), which consists of three oxygen atoms.

A compound is a substance formed when two or more different elements are chemically bonded together, which is not applicable to oxygen in its O2 form as it represents solely one type of element. Therefore, identifying oxygen as a diatomic element correctly captures its molecular nature when it occurs as O2.