What is the oxidation number of oxygen in most compounds?

What is the oxidation number of oxygen in most compounds?

• A. -2 (except -1 for peroxides)
• B. -1
• C. 0
• D. +2

Answer: (A)

Oxidation numbers are a bookkeeping tool for electrons in a compound, and oxygen tends to attract electrons because it is highly electronegative. In most neutral compounds, the rest of the atoms balance to zero by assigning oxygen an oxidation state of -2. This lines up with common examples like water, where hydrogen is +1 on each atom, so oxygen must be -2 to sum to zero. Exceptions exist but don’t change the general rule. In peroxides (such as H2O2), the O–O bond means the two oxygens share electrons differently, giving each oxygen an oxidation state of -1. In compounds like OF2, fluorine is more electronegative than oxygen, pulling electron density away and giving oxygen a positive oxidation state (+2). In superoxides the average oxidation state of oxygen is -1/2 per atom. But for the majority of compounds, oxygen carries -2.

Oxidation numbers are a bookkeeping tool for electrons in a compound, and oxygen tends to attract electrons because it is highly electronegative. In most neutral compounds, the rest of the atoms balance to zero by assigning oxygen an oxidation state of -2. This lines up with common examples like water, where hydrogen is +1 on each atom, so oxygen must be -2 to sum to zero.

Exceptions exist but don’t change the general rule. In peroxides (such as H2O2), the O–O bond means the two oxygens share electrons differently, giving each oxygen an oxidation state of -1. In compounds like OF2, fluorine is more electronegative than oxygen, pulling electron density away and giving oxygen a positive oxidation state (+2). In superoxides the average oxidation state of oxygen is -1/2 per atom. But for the majority of compounds, oxygen carries -2.