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Which among the following are, respectively, the correct oxidation numbers of chloride ion in Cl2O7, Cl2O, ClO3- and ClO2-?

This question was previously asked in
UPSC CAPF 2026 General Ability and Intelligence Question Paper (19-Jul-2026)
The correct answer is

+7, +1, +5, +3

Oxygen is assigned an oxidation number of -2 in each species, and the sum of oxidation numbers must equal the overall charge (0 for a neutral molecule, -1 for a singly charged anion).

In \(Cl_2O_7\): \(2x + 7(-2) = 0 \Rightarrow 2x = 14 \Rightarrow x = +7\).

In \(Cl_2O\): \(2x + 1(-2) = 0 \Rightarrow 2x = 2 \Rightarrow x = +1\).

In \(ClO_3^-\): \(x + 3(-2) = -1 \Rightarrow x = -1 + 6 = +5\).

In \(ClO_2^-\): \(x + 2(-2) = -1 \Rightarrow x = -1 + 4 = +3\).

Hence, the respective oxidation numbers of chlorine are +7, +1, +5, +3.

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