what is the smallest part of a compound called?\nmixture\nelement\nmolecule\natom

Brief Explanations:

A compound is made up of two or more different - elements chemically combined. A molecule is the smallest part of a compound that still has the chemical properties of that compound. A mixture is a combination of substances that are not chemically combined. An element is a pure substance made of only one type of atom. An atom is the smallest part of an element.

Answer:

C. molecule