Which of the following is the smallest part of an element?

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

Answer: (B)

The central idea is how matter is built from basic units. An element is defined by its atoms, and the atom is the smallest unit that still represents the element’s identity. An atom consists of a nucleus and electrons; while electrons are smaller than an atom, they are subatomic particles and do not by themselves define the element. A molecule is two or more atoms bonded together, so it is larger than a single atom. An ion is just an atom that has gained or lost electrons, so it’s the same basic unit—the atom—just with a charge. Therefore, the smallest part of an element is the atom.