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MCQ practice · SSC Chemistry Board questions · Chapter 6: Concept of Mole and Chemical Counting

Chattogram Board 2023

For the reaction in the stimulus:

  1. i. HCl is the limiting reactant
  2. ii. 9.315 g of Al₂O₃ will be left
  3. iii. 24.38 g of AlCl₃ will form

Think it through first, then pick an option.

  1. a i and ii
  2. b i and iii
  3. c ii and iii
  4. d i, ii and iii
Answer and explanation

Correct answer: b i and iii

Al₂O₃ is 0.196 mole and HCl 0.548 mole; ÷ coefficient, HCl is smaller (0.091), so limiting; AlCl₃ = 0.548/3 × 133.5 = 24.38 g; ii is false.

Why the other options are wrong

  • a i and ii: ii is false: 9.315 g is the Al₂O₃ that reacts; what is left is 20 − 9.315 = 10.685 g.
  • c ii and iii: ii is false: 10.685 g of Al₂O₃ is left, not 9.315 g; and i is left out.
  • d i, ii and iii: ii is false: 9.315 g is used up, not left over.