What is the smallest particle of an element or compound that can exist independently while retaining its properties?

The smallest particle of an element or compound that can exist independently while retaining its properties is an atom. An atom is the fundamental unit of a chemical element, consisting of a nucleus surrounded by electrons. Each atom retains the characteristics and chemical properties of the element it represents.

Molecules are formed when two or more atoms bond together, thus representing a combination of atomic structures rather than an independent particle. While compounds are substances formed from two or more different atoms bonded together, they consist of molecules that can contain different types of atoms. Ions are charged particles that can exist independently but do not represent the basic structural unit of an element or compound in its neutral state. Thus, the atom is the correct answer as it is the smallest unit that can exist independently with the inherent properties of the element.