MCQ practice · SSC Chemistry Board questions · Chapter 6: Concept of Mole and Chemical Counting
What is the percentage composition of carbon in propane?
Think it through first, then pick an option.
- a 90%
- b 85.71%
- c 81.82%
- d 18.19%
Answer and explanation
Correct answer: c 81.82%
Propane is C₃H₈: mass 3 × 12 + 8 × 1 = 44; C = (12 × 3 × 100)/44 = 81.82%.
Why the other options are wrong
- a 90%: 90% would need 36 g of carbon in a compound of mass 40. Propane is C₃H₈ with mass 44, so C = (12 × 3 × 100)/44 = 81.82%.
- b 85.71%: 85.71% is 36/42, the carbon of C₃H₆; propane is C₃H₈ (mass 44), so 81.82%.
- d 18.19%: About 18.19% is the share of hydrogen (8/44 ≈ 18.18%); the question asks for carbon, 100 − 18.18 ≈ 81.82%.
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