* Elements are the simplest pure substances that cannot be broken down into simpler substances by ordinary chemical means. They are made up of only one type of atom. Examples include oxygen (O), hydrogen (H), carbon (C), and gold (Au).

* Compounds are formed when two or more different elements chemically combine in a fixed ratio. This combination results in a substance with properties distinct from the original elements.

Water (H₂O) is formed by the chemical combination of two hydrogen atoms and one oxygen atom. It has properties entirely different from hydrogen gas and oxygen gas: it's a liquid at room temperature, essential for life, and has a unique taste and smell.

Therefore, because water is formed from two different elements, it is a compound, not an element.