Boron has primarily two isotopes, one with an atomic mass of 11 amu and another with an atomic mass of 10 amu. If the abundance of the boron atom with a mass of 11 amu is 18.9% and the abundance of the other isotope is 81.1%, what would be the average mass of the boron atom?
A. 10.19 amu
B. 10.81 amu
C. 11 amu
D. 10 amu
E. not enough information given
Answer: A
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