Question

Given that the abundant of isotope $^{54}Fe$, $^{56}Fe$ 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

Answer: (B)

$55.95$

Answer 2

From the given relative abundance, the average weight of Fe
can be calculated as
$A= \frac{ 54 \times 5 +56 \times 90 + 57 \times 5}{100} = 55.95$