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. $55.85u$
• B. $55.95u$
• C. $55.75u$
• D. $55.05u$

Answer 1

Answer: (B)

$55.95u$

Avergae atomic mass of Fe = $\Sigma$ abundance $\times$ atomic mass of isotope

=$\frac{5\times 54+90\times 56+5\times 57}{100}$

=55.95 $u$