Question

Average atomic weight of boron is $10.10$ and boron exists in two isotopic forms $B^{10}$ and $B^{11}$. The percentage abundance of $B^{10}$ is?

• A. $10\%$
• B. $90\%$
• C. $50\%$
• D. $20\%$

Answer 1

The correct option is B $90\%$

Let the percentage in the form of $B^{10}$ is x %

Therefore, the percentage in the form of $B^{11}$ is (100-x) %

Average atomic mass = $x\times \frac{10}{100}+(100-x)\times \frac{11}{100}$

$10.10=\frac{10\times x}{100}+\frac{1100-11x}{100}$

$1010=1100-x$

$x=90$

Therefore, the percentage in which $B^{10}$ exists is 90 %