Answer :
it is most likely that the isotope isnt charged. So i would say there are equal amounts of neutrons as protons.
50 protons + 70 neutrons+ 120 atomic mass of isotope and 50 is the atomic number so i believe its Sn
50 protons + 70 neutrons+ 120 atomic mass of isotope and 50 is the atomic number so i believe its Sn