Calculation of average atomic mass: The atomic attoms fo the two stbale isopes of boron, `._(5)^(10)B (19.78%)` and `._(11)^(5)B (80.22%)`, are `10.0129 u` and `11.0093 u`, respectively, Calculate the average atomic mass of boron.
Strategy : The atomic mass of an element existing in nature as istopes is the weighted average of the istope masses, Thus, multiply the fracton of each isotope by its mass and add these numbers to obtain the mass of born.

Explanation

Converting the percentage to fractions, we have
Average atomic mass of boron
`= (0.1987)(10.0129 u) + (0.8022)(11.009 u) = 10.81 u`