Peroxides have what unusual oxidation number for oxygen?

Peroxides have what unusual oxidation number for oxygen?

• A. -2
• B. -1
• C. 0
• D. +1

Answer: (B)

Oxygen in peroxides carries an oxidation number of -1. This comes from how oxidation numbers are assigned in a neutral molecule like hydrogen peroxide, H2O2. Hydrogen is almost always +1, so the two hydrogens contribute +2. Since the molecule is neutral, the total oxidation numbers must sum to zero, so the two oxygens together must contribute -2. With two oxygens sharing that -2 total, each oxygen has an oxidation number of -1 on average. This is different from the usual -2 for oxygen in most oxides. (Note: in other oxygen species like superoxides the numbers differ, but for common peroxides it’s -1.)

Oxygen in peroxides carries an oxidation number of -1. This comes from how oxidation numbers are assigned in a neutral molecule like hydrogen peroxide, H2O2. Hydrogen is almost always +1, so the two hydrogens contribute +2. Since the molecule is neutral, the total oxidation numbers must sum to zero, so the two oxygens together must contribute -2. With two oxygens sharing that -2 total, each oxygen has an oxidation number of -1 on average. This is different from the usual -2 for oxygen in most oxides. (Note: in other oxygen species like superoxides the numbers differ, but for common peroxides it’s -1.)