Question:
What is the atomic mass of Fe?
Given abundance of
\[
{}^{54}_{26}Fe = 10\%
\]
\[
{}^{56}_{26}Fe = 85\%
\]
\[
{}^{57}_{26}Fe = 5\%
\]
What is the atomic mass of Fe?
Given abundance of \[ {}^{54}_{26}Fe = 10\% \] \[ {}^{56}_{26}Fe = 85\% \] \[ {}^{57}_{26}Fe = 5\% \]
Given abundance of \[ {}^{54}_{26}Fe = 10\% \] \[ {}^{56}_{26}Fe = 85\% \] \[ {}^{57}_{26}Fe = 5\% \]
Show Hint
Average atomic mass is always calculated using weighted mean:
\[
\frac{\sum (\text{mass}\times \text{abundance})}{100}
\]
Updated On: Jun 25, 2026
- \(55.65\)
- \(55.75\)
- \(55.85\)
- \(55.95\)
Show Solution
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The Correct Option is C
Solution and Explanation
Step 1: Use formula for average atomic mass.
Atomic mass is calculated using weighted average: \[ \text{Atomic mass} = \frac{\sum (\text{isotopic mass}\times \text{percentage abundance})}{100} \]
Step 2: Substitute the given values.
\[ \text{Atomic mass of Fe} = \frac{(54\times10)+(56\times85)+(57\times5)}{100} \]
Step 3: Calculate each contribution.
\[ 54\times10=540 \] \[ 56\times85=4760 \] \[ 57\times5=285 \] Adding, \[ 540+4760+285=5585 \]
Step 4: Find the average atomic mass.
\[ \text{Atomic mass} = \frac{5585}{100} \] \[ =55.85 \]
Step 5: Final conclusion.
Hence, the atomic mass of Fe is \[ \boxed{55.85} \]
Atomic mass is calculated using weighted average: \[ \text{Atomic mass} = \frac{\sum (\text{isotopic mass}\times \text{percentage abundance})}{100} \]
Step 2: Substitute the given values.
\[ \text{Atomic mass of Fe} = \frac{(54\times10)+(56\times85)+(57\times5)}{100} \]
Step 3: Calculate each contribution.
\[ 54\times10=540 \] \[ 56\times85=4760 \] \[ 57\times5=285 \] Adding, \[ 540+4760+285=5585 \]
Step 4: Find the average atomic mass.
\[ \text{Atomic mass} = \frac{5585}{100} \] \[ =55.85 \]
Step 5: Final conclusion.
Hence, the atomic mass of Fe is \[ \boxed{55.85} \]
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