What is the fundamental unit of matter called?

The fundamental unit of matter is called an atom because it is the basic building block of all substances. Atoms are the smallest units of elements, which cannot be broken down into simpler substances by ordinary chemical means. Each atom consists of a nucleus, made up of protons and neutrons, surrounded by electrons that orbit around the nucleus. Atoms combine to form molecules, which are made up of two or more atoms bonded together.

While protons and neutrons are indeed crucial components of the atomic structure, they themselves are not considered fundamental units of matter in the same way that atoms are. Protons are positively charged particles found in the nucleus, and neutrons are neutral particles, but without atoms, these particles do not exist in a way that forms matter as we know it. Thus, the atom stands as the smallest entity that retains the properties of an element, making it the fundamental unit of matter.