Chirkut.বাংলা

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

Chattogram Board 2025

The compound B in the stem-

  1. i. aqueous solution is acidic
  2. ii. oxidation number of the central atom is +4
  3. iii. the octet rule is broken in it

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

B = SO₃: it dissolves to give H₂SO₄, so the solution is acidic (i). S is +6, so ii is false. Sulphur holds 12 electrons, an exception to the octet rule (iii).

Why the other options are wrong

  • a i and ii: i is true but ii is false: in B = SO₃ sulphur is +6, not +4. iii is left out: SO₃ breaks the octet rule.
  • b ii and iii: ii is false: S + O₂ → SO₂ (A), SO₂ + O₂ → SO₃ (B). In SO₃, x + 3(−2) = 0 gives x = +6; +4 is the value in SO₂. And i is true, so it cannot be left out.
  • d i, ii and iii: ii is not true: in B = SO₃ sulphur is +6. The +4 belongs to A = SO₂. So not all three are true.

More board questions on this topic