MCQ practice · SSC Chemistry Board questions · Chapter 6: Concept of Mole and Chemical Counting
How many grams of A form from 20 grams of Ca?
Think it through first, then pick an option.
- a 14
- b 21
- c 28
- d 56
Answer and explanation
Correct answer: c 28
A = CaO (2Ca + O₂ → 2CaO); 40 g Ca → 56 g CaO, so 20 g Ca → 28 g.
Why the other options are wrong
- a 14: 14 g is half; A = CaO, 80 g Ca → 112 g CaO, so 20 g → 28 g.
- b 21: 21 g is a slip; 20 × 56/40 = 28 g of CaO.
- d 56: 56 g of CaO comes from 40 g of Ca; 20 g gives 28 g.
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