What does the term "molecule" refer to?

The term "molecule" refers to the smallest unit of a compound that retains all of its chemical properties. This means that a molecule is formed when two or more atoms bond together chemically. Molecules can consist of the same type of atoms, such as oxygen (O2), or different types of atoms, such as water (H2O), which contains hydrogen and oxygen atoms. Understanding that a molecule maintains the characteristics of the compound it represents is crucial in chemistry, as it allows for the study and manipulation of substances at a fundamental level. In contrast, the other options describe different atomic or subatomic entities that do not capture the complete definition and role of a molecule within chemical structures.