Question

Assertion :The oxidation state of superoxide ion in ${KO}_2,{CsO}_2$ and ${RbO}_2$ is $-\frac{1}{2}$. Reason: Since the oxidation state of an alkali metal in any compound is always $+1$, the oxidation state of oxygen is $\frac{1}{2}$ in the $O_2^{-}$ ion.

Read the above assertion and reason and choose the correct option regarding it.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

The oxidation state of superoxide ion in $K{O}_2,Cs{O}_2$ and $Rb{O}_2$ is $\frac{-1}{2}$.

As the oxidation state of alkali metal is never variable. Means it can never change, it remains the same i.e. $+1$.

So if in $K{O}_2$ or $Cs{O}_2$ or $Rb{O}_2$, alkali metal has $+1$ O.S.

Then, Let $O$ have $x$ oxidation state in $M{O}_2$ ( M= alkali metal)

Then $+1+2x=0$

$x=\frac{-1}{2}$

Hence superoxide $O_2^{-}$ has O.S. of $O$ atom to be $\frac{-1}{2}$.