Mass Spectrum of IBr2F The spectrum shows three vertical bars corresponding to the molecular masses labeled on the x-axis. The height of each bar gives the fraction of all molecules having the corresponding mass. Iodine has only a single, stable, naturally-occurring isotope 127I atomic mass 126.90447amu). Fluorine has only a single, stable, naturally-occurring isotope ( 19F atomic mass 18.98840322amu). There are only two stable, naturally-occurring isotopes of bromine (Br). What is the mass of the lighter isotope of Br ? amu 1pts Tries 0/15 What is the mass of the heavier isotope of Br ? amu 1pts Tries 0/15 Select all that are true. 81Br is the less abundant, stable, naturally-occurring isotope of bromine. 79Br is the less abundant, stable, naturally-occurring isotope of bromine. 80Br is the more abundant, stable, naturally-occurring isotope of bromine. 82Br is the less abundant, stable, naturally-occurring isotope of bromine. 77Br is the more abundant, stable, naturally-occurring isotope of bromine. 1pts Tries 0/15