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