The answer is the option (1). the atom has 1 proton. This is because the number of protons is the characteristic that differentiates elements. Only the element hydorgen has 1 proton. It may have zero, one or two neutrons, but the only number for protons is 1. If the atom has a different number of protons it will not be the same element, That is why the periodic table is organized by atomic number which is the number of protons of the atoms of each element.
