MCQ practice · SSC Chemistry Board questions · Chapter 6: Concept of Mole and Chemical Counting
To convert the reactants completely into product, what must be added?
Think it through first, then pick an option.
- a 1.37 g H₂
- b 2 g H₂
- c 12 g F₂
- d 26 g F₂
Answer and explanation
Correct answer: d 26 g F₂
H₂ left = 2 − 1.316 = 0.684 mole; an equal amount of F₂ = 0.684 × 38 = 26 g.
Why the other options are wrong
- a 1.37 g H₂: Adding H₂ only adds to the excess; the shortfall is F₂, 0.684 mole = 26 g.
- b 2 g H₂: H₂ is already in excess; F₂ must be added, 26 g.
- c 12 g F₂: 12 g of F₂ is not enough; the remaining 0.684 mole of H₂ needs 0.684 × 38 = 26 g of F₂.
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