Concept:A pollutant is any substance or form of energy that causes harm or discomfort when released into the environment.Explanation:Smoke contains fine particles and gases that make the air unclean.Sulphur dioxide (SO2) is a toxic gas released from burning fuels and industrial processes.Noise is also a recognized form of pollution because it disturbs the environment.Nitrogen (N2), however, is a natural, harmless gas that makes up about 78% of the atmosphere, so it is not regarded as a pollutant.Answer:Nitrogen (Option B).