Question

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

• A. 10.8
• B. 10.2
• C. 11.2
• D. 10.0

Answer 1

Answer: (A)

Average atomic mass
$=\frac{R.A.\left(1\right)\times M.No+R.A.\left(2\right)\times M.No.}{R.A.\left(1\right)+R.A.\left(2\right)}$
where R.A. = relative abundance
M.No = Mass number
$=\frac{19\times 10+81\times 11}{100}=10.81$