Question

Boron has two stable isotopes, ${}^{10}B\left(19\%\right)$ and ${}^{11}B\left(81\%\right)$. Average atomic weight for boron in the periodic table is:

• A. 10.8
• B. 10.2
• C. 11.2
• D. 10

Answer 1

Answer: (A)

10.8

Average atomic weight $=\frac{\sum \%abundant\times atomicmass}{100}$

$=\frac{19\times 10+81\times 11}{100}=10.81$

Option B is the answer.