What is an article of a substance where it still retains its properties referred to as?

The term that refers to an article of a substance that retains its properties is an atom. An atom is the basic building block of matter and represents the smallest unit of a chemical element. It consists of protons, neutrons, and electrons and retains the chemical properties of the element to which it belongs. This means that when you analyze a single atom of hydrogen, for example, you can identify it as hydrogen due to its specific number of protons, electrons, and neutrons, which determine its chemical behavior.

In contrast, endorphins are naturally occurring peptides in the body that have roles in pain relief and pleasure but do not represent fundamental substances. A module generally refers to a component or unit within a larger system, commonly in contexts like programming or education, and does not fit the description of a substance. An element, while also a correct term that refers to a pure substance that cannot be broken down into simpler substances, typically describes a collection of atoms of the same type rather than a single atom. Thus, while "element" might seem relevant, "atom" specifically denotes the individual unit that retains the properties of that element.