Why are carbon monoxide, nitric oxide, and nitrous oxide exceptions among nonmetal oxides?

Most nonmetal oxides are acidic, meaning they react with water to form oxyacids or with bases to form salts. Carbon monoxide (CO), nitric oxide (NO), and nitrous oxide (N₂O) are considered exceptions because they are neutral oxides; they do not exhibit the typical acidic behavior of reacting with water to form acids or with bases to form salts.12

These compounds are notable for their unique chemical properties:

• Carbon monoxide: Unlike acidic nonmetal oxides, it does not react with water to form an acid.12
• Nitric oxide: It is the most thermally stable oxide of nitrogen and is a paramagnetic molecule, meaning it contains an unpaired electron. This unpaired electron allows it to dimerize into N₂O₂.3
• Nitrous oxide: Often called laughing gas, it acts as a strong oxidizing agent and, unlike typical acidic oxides, supports combustion better than air because it decomposes into nitrogen and oxygen upon heating.3

While many other nitrogen oxides function as acid anhydrides, these specific oxides do not follow the standard acidic classification of nonmetal oxides.13