MCQ practice · SSC Chemistry Board questions · Chapter 7: Chemical Reactions
What is the oxidation number of sulphur in H₂S₂O₇?
Think it through first, then pick an option.
- a + 6
- b − 6
- c + 12
- d − 12
Answer and explanation
Correct answer: a + 6
2(+1) + 2x + 7(−2) = 0, x = +6.
Why the other options are wrong
- b − 6: Wrong sign: S is positive to balance oxygen's negative charge.
- c + 12: +12 is the total for two S atoms; each is +6.
- d − 12: Both sign and size are wrong; each S is +6.
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