What feature distinguishes a polyatomic molecule from a diatomic molecule?

A polyatomic molecule is characterized by being composed of more than two atoms, which can be of the same or different elements. In this context, the distinction between polyatomic and diatomic molecules is clear. Diatomic molecules consist of exactly two atoms, which could either be of the same type (like O₂ or N₂) or different types (like CO or HCl).

The feature that specifically sets polyatomic molecules apart is their complexity, as they can contain three or more atoms that may be arranged in various configurations and include a mixture of different elements – not merely two. This definition encapsulates a wide range of molecules, including common examples like water (H₂O), ammonia (NH₃), and sulfuric acid (H₂SO₄), which contain multiple atoms bonded together.

The option regarding ionic bonds relates to bonding characteristics rather than the number of atoms or types in a molecule, which does not directly differentiate between polyatomic and diatomic molecules. Additionally, the first choice about being composed of only one type of atom inaccurately describes a polyatomic molecule since polyatomic molecules can be heterogeneous. Thus, the distinguishing feature of having more than two different atoms effectively describes polyatomic molecules correctly.