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MCQ practice · SSC Chemistry Board questions · Chapter 7: Chemical Reactions

Dhaka Board 2023

In the stem-

  1. i. The gas produced in vessel A is acidic
  2. ii. The reaction taking place in vessel B is a redox reaction
  3. iii. 1 mole of the compound formed in vessel B = 62 g

Think it through first, then pick an option.

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

Correct answer: c i and iii

HCl on eggshell in A gives CO₂, which is acidic (i). In B, CO₂ + H₂O → H₂CO₃ exchanges no electrons, so ii is false. H₂CO₃ = 2 + 12 + 48 = 62 g/mol (iii).

Why the other options are wrong

  • a i and ii: i is true: CO₂ is acidic. But ii is false: in vessel B, CO₂ + H₂O → H₂CO₃ changes no oxidation number, so it is not redox. iii is left out: 1 mol of H₂CO₃ = 2 + 12 + 48 = 62 g.
  • b ii and iii: ii is false: C stays +4, H +1 and O −2, so the reaction is not redox. And i is true (CO₂ is acidic), so it cannot be left out.
  • d i, ii and iii: ii is not true: CO₂ + H₂O → H₂CO₃ is an addition reaction, but no oxidation number changes, so it is not redox. So not all three are true.

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