Which of the following is the fundamental unit of matter?

• A. Atom
• B. Molecule
• C. Proton
• D. Electron

Answer: (A)

Verified step by step guidance

1. Understand the concept of the fundamental unit of matter: it is the smallest unit that retains the properties of an element.
2. Recall that an atom is the basic building block of all matter, consisting of protons, neutrons, and electrons.
3. Recognize that a molecule is made up of two or more atoms chemically bonded together, so it is not the fundamental unit but a combination of fundamental units.
4. Note that protons and electrons are subatomic particles that make up atoms, but individually they do not represent the smallest unit of matter that retains elemental properties.
5. Conclude that the atom is the fundamental unit of matter because it is the smallest particle that defines the chemical identity of an element.