Here's why:

* Elements are pure substances that cannot be broken down into simpler substances. Examples include carbon, oxygen, and iron.

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

Chalk is primarily made up of calcium carbonate (CaCO3). This means it's formed from the elements calcium (Ca), carbon (C), and oxygen (O) chemically bonded together.

Therefore, chalk is a compound, not an element.