Chlorine 35 and chlorine 37 have __ protons giving the same atomic number.

While they have the same atomic number, isotopes have distinct masses. They are identical in terms of protons and electrons but vary in terms of neutrons. 

For instance, the mass numbers 35 and 37 are shared by two isotopes of chlorine. The atomic number of each is 17. The isotope has 17 electrons, 17 protons, and 18 neutrons with a mass number of 35. The isotope has 20 neutrons, 17 protons, and 17 electrons with a mass number of 37.