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Question

Consider the following statements regarding oxidation numbers:
I. The oxidation number of oxygen in peroxides and superoxides is assigned as -1 and -1/2 respectively.
II. In all its compounds, fluorine has an oxidation number of -1.
III. In a reduction half-reaction, the oxidation number of the reductant decreases.
Which of the statements given above are correct?

This question was previously asked in
NDA 2 2026 GAT Question Paper (13-Sep-2026)
The correct answer is

I and II only

Statement I is correct: in peroxides (e.g., H2O2) oxygen is assigned an oxidation number of -1, and in superoxides (e.g., KO2) it is assigned -1/2. Statement II is correct: fluorine, being the most electronegative element, always has an oxidation number of -1 in all its compounds. Statement III is incorrect: in a reduction half-reaction it is the oxidant (the species being reduced) whose oxidation number decreases, not the reductant's; the reductant itself is oxidised, so its oxidation number increases. Hence, only statements I and II are correct.

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