MCQ practice · SSC Chemistry Board questions · Chapter 6: Concept of Mole and Chemical Counting
Heating 100 g of magnesium carbonate gives 45 g of magnesium oxide. What is the percentage of yield?
Think it through first, then pick an option.
- a 40%
- b 47.62%
- c 84%
- d 94.50%
Answer and explanation
Correct answer: d 94.50%
100 g of MgCO₃ should give 100 × 40/84 = 47.62 g of MgO; (45 × 100)/47.62 = 94.5%.
Why the other options are wrong
- a 40%: 40% just echoes the molecular mass of MgO; the working gives 94.5%.
- b 47.62%: 47.62 is the calculated MgO mass in grams, not the percentage; (45 × 100)/47.62 = 94.5%.
- c 84%: 84 is the molecular mass of MgCO₃; the percentage of yield is 94.5%.
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