Here's why:

* Elements are the simplest forms of matter that cannot be broken down further by chemical means. Examples include carbon (C), hydrogen (H), and oxygen (O).

* Compounds are formed when two or more elements chemically combine in a fixed ratio. Sugar, specifically sucrose, is made up of carbon, hydrogen, and oxygen atoms bonded together in a specific arrangement (C₁₂H₂₂O₁₁).

* Mixtures are combinations of substances that are not chemically bonded. They can be separated by physical means.

Since sugar has a specific chemical formula and is made up of different elements bonded together, it is a compound.