What is the smallest particle of an element that retains all of its properties?

The smallest particle of an element that retains all of its properties is an atom. Atoms serve as the basic building blocks of matter and are the fundamental units that define an element. Each atom consists of a nucleus made up of protons and neutrons, surrounded by electrons in various energy levels.

When we talk about properties, we refer to characteristics such as atomic mass, reactivity, and other physical and chemical properties that are intrinsic to each element. Atoms are unique to each element; for instance, a carbon atom has specific properties that differentiate it from oxygen or hydrogen.

The other options provided do not correctly define the smallest unit that retains the elements' properties. Molecules are formed when two or more atoms bond together, and while they maintain the properties of the compound they represent, they are larger structures. Compounds are substances composed of two or more different elements that are chemically bonded, and thus do not retain the properties of singular elements. The term particle is too vague and does not have a definitive meaning in this context, as it could refer to various components of matter, including atoms, molecules, or subatomic particles.