Which of the following is the smallest particle of any element?

The smallest particle of any element is an atom. An atom is the basic unit that retains the chemical properties of an element. It consists of a nucleus, containing protons and neutrons, surrounded by electrons. Atoms can combine with each other to form molecules or compounds, but they cannot be broken down into smaller units while still maintaining the properties of the element.

Molecules, on the other hand, are formed by the chemical bonding of two or more atoms. Compounds are substances made up of two or more different types of atoms bonded together, and ions are charged particles that can be formed from atoms by gaining or losing electrons. In summary, while all the other options represent larger or different arrangements of atoms, the atom itself is the fundamental building block of all matter.