Iodine has 53 protons. For question 82, the number 127 stands for neutrons plus protons. So the neutron for I-127 is 74. For 83, according to the definition of isotopes, they need to have the same number of protons and different number of neutrons. I-127 and I-131 satisfy these requirements. For 85, the half life of I-131 is 8 days which means after 8 days, only half of sample remains unchanged. So if 80 gram change to 1.25 gram, it goes through 6 half life. So it took 48 days.
