Consider the following observations.(I) pH or rain water is 5.6.(II) Amount of CO2 in the atmosphere is 0.03%.(III) Biochemical oxygen demand is l0 ppm.(IV) EutrophicationPolluted environment is observed under.

(I) pH of water : 5.5 means it is less acidic and contains dissolved CO2. It is not polluted water.(II) CO2 = 0.03% indicated very less pollution.(III) BOD = 10.00 ppm means polluted water.(IV) Eutrophication is the process by which over a period of few years, good quality water bodies are rendered useless as a result of overnutrition due to phosphate nitrates and biomass. Thus, this indicates polluted water.