That is not a non-metallic oxide comprising an oxide of metal elements, mostly acidic oxides, such as typical: water (H2O), sulfur dioxide (SO2), carbon dioxide (CO2), phosphorus pentoxide (P2O5) and the like. Among the non-metallic oxides we are familiar with, carbon monoxide and nitric oxide are not acidic, because of their different nature from acidic oxides, it cannot be classified as acidic oxides as usual. NO2 is not an acidic oxide, neither.
