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Which one of the following compounds is a peroxide?
A
$NO_2$
B
$KO_2$
C
$BaO_2$
D
$MnO_2$
Detailed Solution
A peroxide contains the peroxide ion $O_2^{2-}$ (an –O–O– linkage) with oxygen in the −1 oxidation state.
$BaO_2$: Ba is always +2, so the two oxygens together carry −2, i.e., each O is −1. It contains $O_2^{2-}$ and is a true peroxide (it gives $H_2O_2$ with dilute acid).
$KO_2$: K is +1, so the unit is $O_2^-$, the superoxide ion (oxidation state $-\frac{1}{2}$).
$NO_2$ and $MnO_2$ are normal dioxides with oxygen in the −2 state (N and Mn are +4).
Hence the peroxide is $BaO_2$.
$BaO_2$: Ba is always +2, so the two oxygens together carry −2, i.e., each O is −1. It contains $O_2^{2-}$ and is a true peroxide (it gives $H_2O_2$ with dilute acid).
$KO_2$: K is +1, so the unit is $O_2^-$, the superoxide ion (oxidation state $-\frac{1}{2}$).
$NO_2$ and $MnO_2$ are normal dioxides with oxygen in the −2 state (N and Mn are +4).
Hence the peroxide is $BaO_2$.