Which statement about one atom of an element identifies the element? (1) the atom has 1 proton.
(2) the atom has 2 neutrons.(3) the sum of the number of protons and neutrons in the atom is 3.(4) the difference between the number of neutrons and protons in the atom is 1.

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.