Which statement describes a diatomic molecule?

• A. They must contain two different elements
• B. They are always ionic compounds
• C. They are composed of two atoms
• D. They cannot be formed from the same element

Answer: (C)

A diatomic molecule contains two atoms. That means the molecule is defined by the number of atoms, not whether the atoms are the same or different elements. Examples like H2 and O2 show two atoms of the same element, while CO and NO show two atoms of different elements, yet all are diatomic. Diatomic molecules are formed by covalent bonds, not ionic ones, so they are not restricted to two different elements. Hence the best description is that a diatomic molecule is composed of two atoms.