MCQ practice · SSC Chemistry Board questions · Chapter 7: Chemical Reactions
What is the oxidation value of sulphur in Na₂S₂O₃?
Think it through first, then pick an option.
- a + 2
- b + 4
- c + 5
- d + 6
Answer and explanation
Correct answer: a + 2
2(+1) + 2x + 3(−2) = 0, x = +2.
Why the other options are wrong
- b + 4: Forgetting there are two S atoms gives +4; 2x = 4, so x = +2.
- c + 5: 2 + 2x − 6 = 0 gives +2, not +5.
- d + 6: +6 is S in sulphate; thiosulphate gives +2.
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