The oxidation state of Oxygen in KO2 is
-1/2
We know that the sum of oxidation numbers of all the elements in a compound is equal to 0.
Here the oxidation number of K (Potassium) is +1. So, let the oxidation number of O (oxygen) be x.
If the sum of oxidation numbers of this compound is equal to 0. We get the equation as
+1+2×x=0
2×x=−1
Hence the oxidation number of O (oxygen) is -1/2 or -0.5