Question

Boron has two stable isotopes, ${}^{10}B(19\%)$ and ${}^{11}B(81\%)$. Calculate average atomic weight of boron in the periodic table.

• A. 10.8
• B. 10.2
• C. 11.2
• D. 10.0

Answer 1

Answer: (A)

Average of atomic weight
$=\frac{\%\text{of}{}^{10}B\times \text{atomic mass of}{}^{10}B+\%{\text{of}}^{11}B\times \text{ atomic mass of }{}^{11}B}{\%{\text{ of }}^{10}B+{\text{ of }}^{11}B}$
$=\frac{19\times 10+81\times 11}{19+81}$
$=\frac{190+891}{100}=10.81$