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

The term that describes the smallest unit of an element that retains all the properties of that element is an atom. Atoms are the fundamental building blocks of matter and consist of a nucleus surrounded by electrons. They maintain the characteristics of the element, such as its chemical behavior, reactivity, and physical properties.

In contrast, a molecule is formed when two or more atoms bond together, which may belong to the same element or different elements. An ionic bond refers to the electrostatic attraction between positively and negatively charged ions, which occurs in ionic compounds but does not describe a single unit of an element. A compound consists of two or more different types of atoms bonded together, and therefore does not represent a single element. The unique properties of elements are maintained at the atomic level, making the atom the correct choice in this context.