What does $PPM$ stand for?

Which pollutant from motor-car exhaust causes a mental disease?

Foul smell in the water bodies of tanks,ponds,etc.,is due to:

Which one of the following is not an air pollutant?

In which one of the following have the $BOD$ (Biochemical Oxygen Demand) of sewage $(S)$,distillery effluent $(DE)$,paper mill effluent $(PE)$,and sugar mill effluent $(SE)$ been arranged in ascending order?

In water bodies,fish die due to eutrophication because of the lack of which of the following?