An element is determined by the number of:
Protons
Elements are determined by the number of protons. They are NOT determined by number of electrons, neutrons or nucleons. Only isotopes can have same number of protons. Two different elements cannot have same protons. If number of protons differs then elements should also differ. But this is not the case with number of electrons and neutrons. Thus number of protons are used to identify or determine the elements.