What is the atomic mass of bromine, given the atomic masses and percent abundance of the two isotopes are 78.92 amu (50.7%) and 80.92 amu (49.3%)? Select one:
a. 79.9 amu
b. 78.9 amu
c. 80.9 amu
d. 35 amu

79.9 amu

Explanation:

Given data:

Atomic mass of bromine = ?

Percent abundance of 1st isotope = 50.7%

Atomic mass of 1st isotope = 78.92 amu

Percent abundance of 2nd isotope = 49.3%

Atomic mass of 2nd isotope =80.92 amu

Solution:

Average atomic mass  = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass)  / 100

Average atomic mass = (50.7×78.92)+(49.3×80.92) /100

Average atomic mass =  4001.24 + 3989.36 / 100

Average atomic mass = 7990.6 / 100

Average atomic mass = 79.9 amu.