Which oxidation state is common for oxygen in most compounds?

• A. -2
• B. 0
• C. +1
• D. +2

Answer: (A)

Oxygen almost always carries a -2 oxidation state in most compounds because it is highly electronegative and tends to gain electrons to complete its octet. In typical oxides, water, and many organic and inorganic compounds, oxygen exists as O2− to balance the charges of less electronegative elements. There are a few well-known exceptions that shift this value, such as in peroxides where the O–O bond reduces the oxidation state toward -1 for each oxygen, in compounds with fluorine like OF2 where oxygen ends up with +2, and in superoxide species where the average oxidation state per oxygen is -1/2. But for ordinary oxides and most other oxygen-containing compounds, -2 is the standard oxidation state.