1. By what are isotopes identified? A.mass numbers B.atomic masses C.atomic mass units D.average atomic masses
   

And

1. Uranium atoms each have 92 protons.How many protons does each U-238 atom have?A.92 B.146 C.238 D.330
   

And

1. Chlorine atoms each have 17 protons.How many neutrons does each Cl-37 atom have?A.17 B.20 C.37 D.54