Understand that the basic unit of matter is the smallest component that retains the properties of an element.
Recognize that atoms are the fundamental building blocks of matter, consisting of protons, neutrons, and electrons.
Differentiate between atoms and other entities like ions, molecules, and compounds: ions are charged particles, molecules are groups of atoms bonded together, and compounds are substances formed from two or more different elements.
Recall that atoms can combine to form molecules and compounds, but they themselves are the simplest form of matter.
Conclude that among the given options, atoms are the correct answer as they are the basic units of matter.