Isotope of bromine with atomic mass 79 u = 49.7%
Therefore, Contribution of 35Br79 to atomic mass = (79*49.7)/100 = 39.26 u
Isotope of bromine with atomic mass 81 u = 50.3%
Contribution of 35Br81 to the atomic mass of bromine = (81*50.3)/100 = 40.64u
Hence average atomic mass of the bromine atom = 39.26 + 40.64 u = 80u
Answer
The average atomic mass of the bromine atom = 80u
