What is the basic/smallest unit of matter?

The basic or smallest unit of matter is an atom. Atoms are the fundamental building blocks of all substances, and they make up everything in the universe. Each atom consists of a nucleus, containing protons and neutrons, surrounded by electrons that orbit the nucleus.

While molecules are groups of two or more atoms bonded together, they are not considered the smallest unit of matter because they are composed of multiple atoms. Protons and electrons, on the other hand, are subatomic particles that make up an atom. Although they play critical roles in the structure and behavior of atoms, they are not complete units of matter by themselves. Hence, the atom stands as the smallest unit that retains the properties of an element, which is why it is identified as the basic unit of matter.