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G. The natural isotopic abundance of 10B is 19.60% and 11B is 80.40 %. The exact isotopic masses are 10.13 and 11.009 respectively. Calculate the average atomic mass of boron

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The answer is 10.81 u

Solution :

Relative abundance of 10B isotope =  19.60%

Relative abundance of 11B isotope =   80.40% 

\(Average\space atomic \space mass= {(Mass \space of\space isotope \space 1) \times ( Relative\space abundance \space of \space ^{10}B \space isotope) + (Mass \space of\space isotope\space 2) \times (Relative \space abundance of\space ^{11}B \space isotope \over 100}\) 

=\((10 \times 19.6 ) + (11 \times 80.4 ) \over100\) 

\(={196+ 884.4\over 100}={1080.4\over 100}\) 

=10.804 u 

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