* Elements are pure substances made up of only one type of atom (like oxygen, aluminium, gold, etc.).

* Compounds are formed when two or more different elements chemically combine in a fixed ratio.

In aluminium oxide, you have two different elements: aluminium (Al) and oxygen (O). These elements are chemically bonded together in a specific ratio (2:3). This combination creates a new substance with properties distinct from either aluminium or oxygen alone.