# Oxidation number of oxygen in superoxide ion, ${\text{O}}_{\text{2}}^ -$ is:(A) $-2$ (B) $-\dfrac{1}{2}$ (C) $-\dfrac{3}{2}$ (D) none of these

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Hint: In an ion, the sum of the oxidation numbers of all the atoms is equal to zero. In superoxide ion, having two oxygen atoms and a unit negative charge, the sum of the oxidation numbers of two oxygen atoms is - 1.

The chemical formula of superoxide ion is ${\text{O}}_{\text{2}}^ -$. It contains two oxygen atoms and a negative charge.
Let x be the oxidation number of oxygen in superoxide ion, ${\text{O}}_{\text{2}}^ -$.
Calculate the oxidation number of oxygen in superoxide ion, ${\text{O}}_{\text{2}}^ -$
x = $- \dfrac{1}{2}$
Hence, the oxidation number of oxygen in superoxide ion, ${\text{O}}_{\text{2}}^ -$ is $- \dfrac{1}{2}$ .