Which of the following is the basic unit of matter?

• A. Molecule
• B. Element
• C. Atom
• D. Compound

Answer: (C)

Matter is built from atoms, the smallest unit that still carries the properties of an element. An atom has a central nucleus made of protons and neutrons, with electrons orbiting around it, and this structure is what defines the element. Atoms can join with other atoms to form molecules, which are simply two or more atoms bonded together. An element is a pure substance made of only one kind of atom, while a compound is formed when two or more different elements combine in a fixed ratio. Because the question asks for the smallest piece that retains the nature of matter, the atom is the best answer.