The part of the atom that can be used to identify it is the atomic number, which corresponds to the number of protons in the nucleus of the atom. The atomic number is unique to each element and determines its identity. For example, all atoms with six protons are carbon atoms, regardless of the number of neutrons or electrons they have.
The periodic table of elements is arranged based on the atomic number of each element, which allows scientists to easily identify and classify different atoms. The atomic number provides crucial information about an atom's properties and its behavior in chemical reactions.