Final answer:
The identity of an atom is determined by its number of protons, which defines the chemical element to which the atom belongs.
Step-by-step explanation:
The identity of an atom is determined by the number of protons it contains. Protons are subatomic particles with a positive charge and, along with neutrons and electrons, are one of the three main components of an atom. The number of protons in the nucleus of an atom defines the chemical element to which the atom belongs, and this number is called the atomic number. For example, all atoms with one proton are hydrogen atoms, while those with six protons are carbon atoms. The electrons, which carry a negative charge, and the neutrons, which have no charge, do not determine the atom's identity but do influence other properties like its stability and chemical behavior.