Question

Given that the abundances of isotopes ${}^{54}Fe{,}^{56}Fe$ and ${}^{57}Fe$ are $5\%,90\%$ and $5\%$ respectively, the atomic mass of $Fe$ is:

• A. $55.85$
• B. $55.95$
• C. $55.75$
• D. $56.05$

Answer 1

The correct option is B $55.95$

$\overline{A}=\frac{\sum A_i{x}_i}{\sum x_i}$
$\overline{A}=54\times 0.05+56\times 0.90+57\times 0.05$
$\overline{A}=55.95$