The smallest particle of a substance where it still retains its properties is a/an?

The smallest particle of a substance that retains its properties is indeed a molecule. A molecule consists of two or more atoms that are chemically bonded together, and it represents the fundamental building block of a chemical substance. For instance, in the case of water, each water molecule is made up of two hydrogen atoms and one oxygen atom. This combination creates the properties of water, which cannot be simply obtained through its individual hydrogen or oxygen atoms alone.

Atoms, while they are the basic unit of a chemical element, do not represent the smallest particle that retains the unique properties of a compound or molecule; they are the components that make up molecules. Ions are charged particles that result when atoms gain or lose electrons, and while they can exist independently, they do not represent a stable form of matter that retains the properties of a compound. Compounds are substances made of two or more different types of atoms bonded together in fixed proportions, but a compound itself is made up of molecules. Therefore, the correct focus on molecules as the smallest particle that retains the properties of a substance is accurate in this context.