Question

Boron has two isotopes ¹⁰B and ¹¹B with atomic masses 10 and 11, respectively. If its average atomic mass is 10.81, the abundance of ¹⁰B is ____________.

Options

• 20%

• 81%

• 19%

• 80%

Answer 1

Boron has two isotopes ¹⁰B and ¹¹B with atomic masses 10 and 11, respectively. If its average atomic mass is 10.81, the abundance of ¹⁰B is 19%.

Explanation:

Average atomic mass = `("atomic mass of"  ""^10"B" xx "percentage atomic mass of"  ""^11"B" xx "percentage")/100`

Let the % abundance of ¹⁰B isotope = x

% abundance of ¹¹B isotope = 100 − x

Average atomic mass = 10.81

From formula, Average atomic mass

= `(10 xx "x" + 11 xx (100 - "x"))/100` = 10.81

10 x + 1100 − 11x = 10.81 × 100

−x = −1100 + 1081

x = 19

Percentage abundance of ¹⁰B = 19%