Final answer:
Oxygen represented as O₂ is a diatomic molecule, meaning it is composed of two atoms of the same element, oxygen. Altering the subscript changes the identity of the substance, as the subscript indicates the number of each type of atom.
Step-by-step explanation:
The student is asking about the type of matter for oxygen (₂₂), which is a diatomic molecule. A diatomic molecule is a molecule composed of only two atoms, in this case, two oxygen atoms. This is not a compound because it contains only one type of element. The subscript in the chemical formula indicates the number of atoms of each element present in the smallest unit of the substance. Here, the subscript '2' indicates there are two oxygen atoms. Remember, subscripts should not be altered as it changes the identity of the substance.
The way we describe different molecules using these subscripts is key for understanding how to represent chemical species. For example, carbon dioxide has the formula CO₂, indicating one carbon atom and two oxygen atoms in each molecule. This differs from carbon monoxide, which has a formula of CO, indicating one carbon atom and one oxygen atom per molecule.