What are the smallest units of matter?

• A. An Atom
• B. Molecules and Atoms
• C. Electrons
• D. An Ion

Answer: (B)

Matter is built from tiny building blocks, and these come in two fundamental forms: atoms, which are the basic units of elements, and molecules, which are groups of two or more atoms bonded together to form compounds. An atom by itself represents the smallest unit that retains the properties of an element, while a molecule is the smallest unit that retains the properties of a compound. Because some substances are pure elements and others are compounds, the most complete answer to “smallest units of matter” includes both atoms and molecules. For example, oxygen gas is made of O atoms, while water is a molecule made of H and O atoms bound together. Electrons are subatomic particles and aren’t the smallest units of matter in this context, and an ion is simply a charged atom or molecule, not a distinct smallest building block.