Bromine, with atomic mass 79.942 u, is composed of nearly equal amounts of two isotopes, one of which contains 79 nucleons per atom.The mass number of the other isotope is:
A)78
B)79
C)80
D)81
E)82

Question

Quizplus · Accepted Answer

The average atomic mass of bromine is 79.942 u, which is close to 80. Since one isotope has a mass number of 79, the other must be 81 to average out to approximately 80 when considering their nearly equal abundance.

Bromine, with Atomic Mass 79