A chemical combination of simple substances is called a compound.

Here's why:

* Simple substances are elements, made up of only one type of atom (like oxygen, carbon, or gold).

* Compounds are formed when two or more different elements chemically combine in a fixed ratio. This means the atoms of different elements are held together by chemical bonds.

Examples:

* Water (H₂O) is a compound formed by the chemical combination of hydrogen and oxygen.

* Salt (NaCl) is a compound formed by the chemical combination of sodium and chlorine.

Let me know if you have any other questions!