* Element: A pure substance consisting of only one type of atom (e.g., gold, oxygen).

* Compound: A substance formed when two or more different elements chemically combine in a fixed ratio (e.g., water (H₂O), carbon dioxide (CO₂)).

* Mixture: A combination of two or more substances that are not chemically bonded and can be separated by physical means (e.g., salt and pepper).

Water vapor is simply water (H₂O) in its gaseous state. Water is formed by the chemical combination of two hydrogen atoms and one oxygen atom. This fixed ratio and the chemical bond between the atoms makes water a compound.