Question

Boron has two isotopes, ${}^{10}B$ and ${}^{11}B$ whose relative abundances are $20$% and $80$% respectively. Atomic weight of boron is:

• A. $10$
• B. $11$
• C. $10.5$
• D. $10.8$

Answer 1

Answer: (D)

$10.8$

Average atomic weight $=\frac{20\times 10+80\times 11}{100}=\frac{200+880}{100}=\frac{1080}{100}=10.8g$