Robert is studying a substance that is a made out of one element this means that

Answer: it means that Robert is studying a simple substance.

Explanation:

A simple substance can be a raw material, an atom, or an chemical element. It is an exhaustive investigation of only one element that is part of all the study subject. It's important that when someone study only an element know that it can be a potencial part of a big factor, to be a gratest function inside the world.