What is a pure substance composed entirely of one type of atom?

A pure substance composed entirely of one type of atom is classified as an element. Elements are the fundamental building blocks of matter and cannot be broken down into simpler substances through chemical means. They are listed on the periodic table and each element has a unique set of properties that distinguish it from others.

For example, carbon, oxygen, and gold are all elements composed of only one kind of atom. This distinct identity is important in chemistry as it allows for the categorization and study of various substances based on their atomic structure.

In contrast, a compound consists of two or more different types of atoms chemically bonded together, forming molecules. A mixture, on the other hand, contains two or more substances that are physically combined but retain their individual properties. A solution is a specific type of mixture where one substance (the solute) is dissolved in another (the solvent), resulting in a homogeneous mixture. Only elements maintain the characteristic of being entirely composed of a single type of atom, which is why the correct answer is the identification of an element.