How many atoms in a mole of iodine?

Most isotopes of iodine have half lifes ranging typically between a few nanoseconds and a couple of hours. A handful of isotopes can be expected to last for roughly two weeks, and the only stable isotope of iodine is 127I. Assuming then that you mean stable iodine, the relevant numbers are isotope 127 and element number 53 in the Periodic Table meaning that stable iodine has 127 particles in the core of which 53 are protons. From this we can deduce that one atom of 127I has 127 - 53 = 74 neutrons.

I leave it as an exercise to calculate the number of neutrons found in three atoms of iodine.