Answer:
pure substance
Step-by-step explanation:
Mixture : It is defined as the substance that is made by the combination of two or more different components.
Pure substance : It is defined as a substance that is made by the combination of only one type of atom or only one type of molecule.
Element : It is a pure substance which is composed of atoms of similar elements.
Compound : It is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass. Pure compounds are the one which has same elements combining and the impure are the one which has different elements combining.
As per question, the pure substance when it is composed of atoms best describes the element,