MCQ practice · SSC Chemistry Board questions · Chapter 7: Chemical Reactions
What is the oxidation number of Cl in HClO₄?
Think it through first, then pick an option.
- a + 1
- b + 3
- c + 5
- d + 7
Answer and explanation
Correct answer: d + 7
(+1) + x + 4(−2) = 0, x = +7.
Why the other options are wrong
- a + 1: +1 is H's value; for Cl, 1 + x − 8 = 0 gives +7.
- b + 3: +3 cannot balance four O at −8; x = +7.
- c + 5: +5 would be in HClO₃; HClO₄ gives +7.
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