Which statement describes Nitrogen Oxide?

• A. A combination of nitrogen and oxygen; used for the combustion of fossil fuels in vehicles and power plants
• B. A gas that only forms in the atmosphere
• C. A salt formed from nitrogen and oxygen
• D. A liquid oxide used in water treatment

Answer: (A)

Nitrogen oxide is a gas formed when nitrogen from the air reacts with oxygen at high temperatures during combustion. When fossil fuels burn in engines and power plants, the heat allows this reaction to occur, producing nitrogen oxides as part of the exhaust. This fits the description of being a combination of nitrogen and oxygen and links it directly to combustion processes in vehicles and power plants. The other statements aren’t right: nitrogen oxide isn’t something that only forms in the atmosphere, isn’t a salt, and isn’t a liquid oxide used in water treatment.