The oxidation number of oxygen in H2 O2 (A) -1 (B) -2 (C) -3 (D) -1/2

Rules for Assigning Oxidation Number 

• All elements have a zero oxidation number when they are in their free state.
• Fluorine, which has the highest electronegative charge, has an oxidation number of -1 in all compounds.
• Monoatomic ions have an oxidation number equal to their charge. For instance:
• Li+, Ca2+, and Al3+ have oxidation states of +1, +2, and +3, respectively.
• Cl- and SO42- have oxidation states of 1 and 2, respectively.
• All compounds, with the exception of ionic hydrides, have hydrogen in the +1 oxidation state (-1 oxidation state).
• Except for peroxides, which have an oxidation state of 1, oxygen is in a compound in a -2 state.
• Alkaline earth metals (Be, Mg, etc.) have +2 oxidation states, while alkali metals (Li, Na, K, etc.) always have a +1 oxidation state.
• The charge of the ligands is considered in transition metal complexes.
• The ligands can be divided into neutral, cationic, and anionic types. The neutral ligands are charge-free.
• Hydrogen peroxide, or H2O2.
• Peroxides are substances in which two oxygens are linked together by the bond O-O.
• There are two hydrogen atoms in the molecule hydrogen peroxide, meaning that its two negative charges are balanced by its two positive hydrogen ion charges.
• Therefore, the combined charge of two oxygen atoms is negative.
• In that regard, we might argue that each oxygen bears a charge = -2/2 = -1 because the molecule is neutral overall.

Summary:

The oxidation number of oxygen in H2 O2, (A) -1 (B) -2 (C) -3 (D) -1/2

The oxidation number of oxygen in H2 O2 is -1. The oxidation number can be found by knowing the number of charges which are assigned to an atom.