What is the purest part of a substance that can be broken down and retains its properties as that element?

The purest part of a substance that can be broken down and still retains its properties as that element is an element itself. An element is defined as a fundamental substance that cannot be simplified or broken down into simpler substances through chemical means. Each element consists of only one type of atom, which means its unique properties are inherent to that specific type of atom.

In contrast, a compound consists of two or more elements that are chemically bonded together and can be separated into simpler substances through chemical reactions. While molecules refer to the combination of atoms (which can be of the same or different elements), they do not represent the single, purest form of a substance. Mixtures, on the other hand, involve two or more substances that are physically combined and can vary in composition, lacking the consistent properties of pure elements or compounds.

Thus, the element stands out as the most fundamental constituent, embodying the purest form that retains its identity and properties in any instance as an individual type of atom.