What can nitrogen combine with to form NOx?

Nitrogen can combine with oxygen to form nitrogen oxides, commonly referred to as NOx. This reaction particularly occurs at high temperatures, such as those found in combustion processes like those in gas furnaces, automotive engines, and power plants. The presence of sufficient oxygen facilitates the reaction between nitrogen and oxygen, leading to the formation of various types of nitrogen oxides, including nitrogen monoxide (NO) and nitrogen dioxide (NO2), which are significant contributors to air pollution and smog.

The other options do not play a direct role in the formation of NOx. Carbon dioxide, while a product of combustion, does not react with nitrogen to form nitrogen oxides. Hydrogen can participate in various chemical reactions but does not combine with nitrogen and oxygen to produce NOx. Similarly, hydrocarbons, which consist mainly of carbon and hydrogen, do not directly contribute to the formation of NOx, though they can participate in combustion reactions. Therefore, the combination of nitrogen and oxygen is the primary pathway for NOx formation.