MCQ
Given that the abundances of isotopes ${ }^{54} \mathrm{Fe},{ }^{56} \mathrm{Fe}$ and ${ }^{57} \mathrm{Fe}$ are $5 \%, 90 \%$ and $5 \%$, respectively, the atomic mass of $\mathrm{Fe}$ is
- A$55.85$
- ✓$55.95$
- C$55.75$
- D$56.05$
✓
Answer
Correct option: B.
$55.95$
b
Avergae atomic mass of Fe $=$ $\sigma$ abundance $\times$ atomic mass of isotope
Avergae atomic mass of Fe $=$ $\sigma$ abundance $\times$ atomic mass of isotope
$=\frac {5 \times 54 + 90 \times 56 + 5 \times 57} {100} =55.95 \ u$
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