A molecule is made up of two or more ________.

• A. Ions
• B. Atoms
• C. Elements
• D. Molecules

Answer: (B)

A molecule is formed when two or more atoms bond together to form a single unit with its own properties. That makes atoms the correct fill because the defining idea is that molecules are built from atoms bonded together. Ions are charged particles and don’t define a molecule by themselves; elements are pure substances that can exist as single atoms or as groups of atoms, but a molecule specifically refers to a bonded collection of atoms. For example, water is a molecule because it consists of two hydrogen atoms bonded to one oxygen atom, while O2 is a molecule of two oxygen atoms; table salt, though, is an ionic compound made of ions, not a discrete molecule in the solid form.