Question

Atomic mass of boron is 10.81 amu. It has two isotopes with 80% and 20% abundance respectively. The atomic mass of one isotope is 11, the mass of other isotope is:

• A. 10.81
• B. 11.01
• C. 10.05
• D. 21.82

Answer 1

Answer: (C)

10.05

Atomic mass of Boron $=10.81$

duppose mass of other isotope$=m$

mass of one isotope $=11$

$11\times 80\%+m\times 20\%=10.81$

$\frac{11\times 80+m\times 20}{100}=10.81$

$880+20m=1081$

$20m=1081-880=201$

$m=\frac{201}{20}=10.05$