The following are examples of what? H2O, N2, H2, O3

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

Answer: (B)

A molecule is a group of two or more atoms held together by chemical bonds. The items listed—H2O, N2, H2, and O3—are all discrete units formed by bonding atoms: water consists of two hydrogens and one oxygen in a single bonded unit, nitrogen gas is two nitrogen atoms bonded together, hydrogen gas is two hydrogen atoms bonded together, and ozone is three oxygen atoms bonded in a single molecule. They are not single atoms, and they are not charged particles (ions), though they are all chemicals; the defining idea here is that each example is a molecule—a stable cluster of atoms functioning as one unit.