Answer:
86.56 g/mol is the average atomic mass of the element X
Explanation:
The average atomic mass of an element is defined as the sum of the masses of each isotope times its percentage. For the element X the average atomic mass is:
85.91×67.25% + 87.91×32.75%
85.91×0.6725 + 87.91×32.75
86.56 g/mol is the average atomic mass of the element X
