GATE 2017 ME (ME2) – Question 32
Given atomic weights Fe = 56 and C = 12, the carbon weight percentage in cementite Fe₃C is ______.
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Correct answer: 6.3 to 7.0
Explanation
One formula unit contains iron mass3·56=168 and carbon mass12, for total180 in consistent atomic-mass units. The carbon weight fraction is12/180, so carbon percentage is100·12/180=**6.667%**. The atom fraction1/4 would not be the weight fraction.