DDT is not soluble in water but soluble in fats. Aquatic micro-organisms absorb them in fats where they accumulate to form concentration many times greater than in water. Zooplankton accumulate more concentrations, fishes feeding on zooplanktons also accumulate more concentration and finally birds feeding on fishes contain these compounds in more concentration. This increase in accumulation of toxic substances in the food pyramids is called "Biological magnification."

Correct Option: B

DDT is not soluble in water but soluble in fats. Aquatic micro-organisms absorb them in fats where they accumulate to form concentration many times greater than in water. Zooplankton accumulate more concentrations, fishes feeding on zooplanktons also accumulate more concentration and finally birds feeding on fishes contain these compounds in more concentration. This increase in accumulation of toxic substances in the food pyramids is called "Biological magnification."

Release of mercury in water causes pollution. Mercury enters the food chain killing fishes. Human beings feeding on such fishes will suffer from minamata disease. Similarly all carnivores feeding on fishes will develop this disease except rabbit because it is herbivore.

Correct Option: B

Release of mercury in water causes pollution. Mercury enters the food chain killing fishes. Human beings feeding on such fishes will suffer from minamata disease. Similarly all carnivores feeding on fishes will develop this disease except rabbit because it is herbivore.

By dumping of huge amount of sewage, the oxygen levels are depleted, which are reflected in terms of BOD values of water. The number of microbes also increases tremendously and these also consume most of the oxygen. Thus BOD of the river water will increase.

Correct Option: A

By dumping of huge amount of sewage, the oxygen levels are depleted, which are reflected in terms of BOD values of water. The number of microbes also increases tremendously and these also consume most of the oxygen. Thus BOD of the river water will increase.

Organic pollutants brought in by the sewage drained into water bodies provides nutrients for stimulating growth of algae. Algal bloom reduces availability of light to the submerged plants which get killed. Dead algae and dead submerged plants consume oxygen during decomposition, causing oxygen depletion and increases competition for oxygen.

Correct Option: D

Organic pollutants brought in by the sewage drained into water bodies provides nutrients for stimulating growth of algae. Algal bloom reduces availability of light to the submerged plants which get killed. Dead algae and dead submerged plants consume oxygen during decomposition, causing oxygen depletion and increases competition for oxygen.

Part of fertilizers containing phosphates are passed down into water bodies as surface run off. Sewage contamination also results in algal bloom (eutrophication) due to increased availability of nitrate and phosphate.

Correct Option: D

Part of fertilizers containing phosphates are passed down into water bodies as surface run off. Sewage contamination also results in algal bloom (eutrophication) due to increased availability of nitrate and phosphate.