What distinguishes a compound from a molecule?

A compound is defined as a substance that consists of two or more different kinds of atoms chemically bonded together. This definition highlights the key distinction between compounds and molecules. While all compounds are molecules, not all molecules are compounds. For instance, a molecule can consist of two atoms of the same element, such as O2 (oxygen gas), which does not qualify as a compound because it contains only one type of atom.

The other options are misleading because compounds can exist in various states (solid, liquid, or gas) depending on their specific properties and the conditions they are under. Therefore, it is not accurate to say that compounds are always solid or that they cannot be gaseous.