Which of the following best completes the statement: The smallest unit of matter is a(n) ________.

• A. molecule
• B. atom
• C. proton
• D. electron

Answer: (B)

Verified step by step guidance

1. Understand the definition of the smallest unit of matter: It is the fundamental building block that retains the properties of an element.
2. Recall that an atom is the smallest unit of an element that maintains its chemical identity.
3. Recognize that a molecule is made up of two or more atoms bonded together, so it is larger than an atom.
4. Note that protons and electrons are subatomic particles, which are components of an atom, but not units of matter by themselves.
5. Conclude that the correct completion of the statement is 'atom' because it is the smallest unit of matter that retains the properties of an element.