Which of the following is the smallest unit of an element that retains all the chemical properties of that element?

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

Answer: (D)

Verified step by step guidance

1. Understand the question is asking for the smallest unit of an element that retains all its chemical properties.
2. Recall that a proton is a subatomic particle found in the nucleus of an atom, but alone it does not represent the element's chemical properties.
3. Recall that an electron is a subatomic particle orbiting the nucleus, but alone it does not define the element's chemical properties.
4. Recall that a molecule is a group of atoms bonded together, which can be of the same or different elements, so it is not the smallest unit of a single element.
5. Recognize that an atom is the smallest unit of an element that retains all the chemical properties of that element, as it contains protons, neutrons, and electrons arranged in a way that defines the element.