Chirkut.বাংলা

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

Cumilla Board 2022

What is the oxidation number of sulphur in sodium thiosulphate?

Think it through first, then pick an option.

  1. a +½
  2. b + 1
  3. c + 2
  4. d + 4
Answer and explanation

Correct answer: c + 2

In Na₂S₂O₃, 2(+1) + 2x + 3(−2) = 0, so 2x = 4 and x = +2.

Why the other options are wrong

  • a +½: No fraction arises; 2(+1) + 2x − 6 = 0 gives x = +2.
  • b + 1: +1 is the value of Na; for S, 2x = 4 so x = +2.
  • d + 4: Forgetting there are two S gives +4; 2x = 4, so each S is +2.

More board questions on this topic