What is the oxidation number of oxygen in compounds?

The oxidation number of oxygen in most compounds is typically -2. This convention is rooted in the fact that oxygen usually forms two bonds by sharing its six valence electrons, allowing it to achieve a stable electron configuration akin to that of noble gases. When oxygen forms compounds, it often gains two electrons, leading to its common oxidation state of -2.

For example, in water (H₂O) and carbon dioxide (CO₂), oxygen has an oxidation number of -2. This general rule applies in most situations, such as in oxides and other compounds containing oxygen.

While there are exceptions, such as peroxides (e.g., hydrogen peroxide, H₂O₂) where the oxidation state of oxygen is -1, and superoxides where it could be -1/2, the predominant and most recognized oxidation state for oxygen remains -2 in the majority of chemical compounds. This makes -2 the correct and relevant choice in the context of general oxidation numbers for oxygen in compounds.