Here's why:

* Compound: A substance formed when two or more different elements are chemically combined in a fixed ratio. This chemical change results in a new substance with properties distinct from the original elements. For example, water (H₂O) is a compound formed from the elements hydrogen and oxygen.

* Mixture: A combination of two or more substances where each substance retains its individual properties. Mixtures can be separated by physical means. For example, sand and water form a mixture.

Let me know if you have any other chemistry questions!