Biochemical Oxygen Demand (BOD) is the amount of oxygen required (in ppm)

So₂ is the component of classical smog.

Complete reaction of acid rain is

$2S{O}_2+O_2+2H_{2}O\stackrel{}{\to }2H_{2}S{O}_4\left(acidrain\right)$  

BOD value less than 5ppm is considered as clean water and BOD value more than 10ppm is considered as polluted water.

Veronal is a barbiturate drug and it constitutes an important class of tranquilizers.

It is process in which nutrient enriched water bodies support a dense plant population which kills animal life by depriving it of oxygen and result in subsequent loss of biodiversity is known as Eutrophication.