What is the smallest particle called that can still retain the properties of a substance?

The smallest particle that can still retain the properties of a substance is referred to as an atom. Atoms are the fundamental building blocks of matter and consist of a nucleus surrounded by electrons. Each element on the periodic table is made up of atoms, and the arrangement and types of these atoms determine the properties of the substance they make up.

For example, while molecules consist of two or more atoms bonded together, they can exhibit properties that may differ from the individual atoms that compose them. The term "electron" refers specifically to a negatively charged subatomic particle that is part of an atom, but it does not represent a particle that can independently express the properties of the overall atom or substance. A compound is a chemical substance formed when two or more different types of atoms bond together, which means it requires the presence of multiple atoms to exist.

Thus, the atom is the most basic unit that retains the essential characteristics of its corresponding element, making it the correct answer to the question.