We know potassium which is a member of group 1 and thus it can naturally react with oxygen. Again we know KO2 is an super oxide and its is an neutral molecule so it has a net charge of zero.

Let x be the oxidation state of Oxygen. Thus we can write,

1+2x=0 where +1 is the oxidation state of potassium

thus, x=-1/2

Thus the oxidation state of oxygen in KO2 is -0.5.

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