Nitrogen oxides are a portion of matter consisting of compounds of nitrogen and oxygen. It is a collective term for numerous oxides of nitrogen with a gaseous normal state of matter. They can act as air pollutants.
Nitric oxide is a portion of matter with the chemical formula NO. It is a gas and can act as an air pollutant. Synonyms are nitrogen oxide or nitrogen monoxide.
A portion of matter is an aggregate of material entities that have a state of matter.
Editor note:
Portions of matter describe mass nouns like e.g. water, air and fuel. Mass nouns are uncountable, but portions of these can be quantified, like 1 glass of water, 1 m³ of air or 1 barrel of fuel. For further explanation please refer to: https://github.com/OpenEnergyPlatform/ontology/wiki/Explanation-on-mass-nouns
Ontology