Here's why:

* Elements: The fundamental building blocks of matter (like hydrogen, oxygen, carbon, etc.).

* Fixed Ratio: A compound is formed when two or more elements chemically combine in a specific, unchanging ratio. For example, water (H₂O) always has two hydrogen atoms for every one oxygen atom.

Examples of compounds:

* Water (H₂O)

* Salt (NaCl)

* Sugar (C₁₂H₂₂O₁₁)

* Carbon dioxide (CO₂)

Let me know if you have any other chemistry questions!