Soot is an example of: A. a primary pollutant
Primary pollutant refers to a pollutant that come up directly from the source. Soot is created when we burn organic compounds into black substances consisting of amorphous carbon.
Without being burned, organic compounds are not considered as pollutant. Since the creation of soot does not happen because of the chain reaction caused by other pollutant, we can consider soot as a primary pollutant.