What is defined as the smallest unit of matter that retains the properties of a given element?

The smallest unit of matter that retains the properties of a given element is defined as an atom. Atoms are the building blocks of matter, and each element on the periodic table is made up of its own unique type of atom. For example, a carbon atom retains all the distinctive characteristics of carbon as an element, while an oxygen atom maintains the properties of oxygen.

Atoms consist of protons, neutrons, and electrons, and their arrangement determines the specific chemical and physical properties of the element. Other terms in the choices refer to larger groupings of matter; a molecule is a group of atoms bonded together, typically representing a compound when it consists of different elements. A compound itself is formed when two or more different types of atoms combine chemically. An element refers to a substance that cannot be broken down into simpler substances and is identified by the type of atom it contains. Thus, an atom is the fundamental unit that embodies the characteristics of an element.