Which of the following statements about diatomic molecules is true?

• A. They can only be found as ions.
• B. They must contain two different elements.
• C. They always exist as crystalline solids at room temperature.
• D. They consist of two atoms of the same element in the molecule.

Answer: (D)

A diatomic molecule is formed when two atoms are joined together. This is true for both kinds: some diatomic molecules have two identical atoms, like O2 or N2, while others are made from two different elements, like CO or NO. So the idea that diatomic molecules consist of two atoms of the same element is true for the homonuclear examples you often see, but it isn’t universal to all diatomic molecules. The other statements aren’t generally true: diatomic molecules aren’t limited to ions, they don’t have to be solid at room temperature (many are gases), and being two atoms long is the key feature, not that the atoms must always be the same.