What is the oxidation number of oxygen in hydrogen peroxide (H2O2)?

In hydrogen peroxide (H2O2), the oxidation number of oxygen is -1. This is derived from the rules governing oxidation states. Typically, oxygen has an oxidation state of -2 in most compounds; however, in peroxides, which is the category hydrogen peroxide belongs to, the oxidation state changes due to the unique bonding characteristics of the peroxide ion (O-O linkage).

In H2O2, the two oxygen atoms share a single bond with each other, and as a result, they do not exhibit the typical -2 oxidation state. Instead, each oxygen in the peroxide has an oxidation state of -1. To confirm this, if we assign the oxidation state of hydrogen as +1 (which is generally how it behaves), we can see that the overall charge on the molecule must equal zero (since it is a neutral molecule). Therefore, the total contributions from the two hydrogens (+2) must be balanced by the contributions from the two oxygens, leading to the conclusion that each oxygen is indeed at -1. Thus, the correct oxidation number for oxygen in hydrogen peroxide is -1.