What is the smallest unit of an element that retains the properties of that element?

The smallest unit of an element that retains all of the properties of that element is an atom. Atoms are the foundational building blocks of matter and consist of protons, neutrons, and electrons. Each element on the periodic table is defined by its unique atomic structure, which determines its chemical properties and behavior. For instance, the characteristics of oxygen, hydrogen, or carbon can be directly attributed to the structure and behavior of their constituent atoms.

Molecules, on the other hand, are formed when two or more atoms bond together, and while they may exhibit properties related to the elements they are composed of, they do not represent the smallest individual unit of each element. Compounds involve different elements chemically bonded together, which means they are not representative of a single element's properties. Ions are atoms or molecules that have gained or lost one or more electrons, resulting in a net charge. While related to atoms, they do not retain the unaltered properties of the element in its neutral state.

Overall, an atom is the fundamental entity that embodies the characteristics and traits of each element within the realm of chemistry and biology.