Question

Which of the following is not a rule for calculating oxidation number ?

• A. For ions, oxidation number is equal to the charge on the ion.
• B. The oxidation number of oxygen is -2 in all of its compound.
• C. The oxidation number of fluorine is -1 in all of its compounds.
• D. Oxidation number of hydrogen is +1 except in binary hydrides of alkali metals and alkaline earth metals where it is -1.

Answer 1

The correct option is B The oxidation number of oxygen is -2 in all of its compound.

In many cases oxygen has the charge $-2$. But in some compounds like peroxides and superoxides which are the exceptional cases, the oxidation state is not $-2$.

In peroxides like hydrogen peroxide, benzoyl peroxide, oxidation state of oxygen is $-1$, whereas in superoxide, it is $-1/2$.