JEE Main levelSingle correct optionDifficulty 2 of 3ev178
Run-off of fertilisers rich in nitrate and phosphate into a pond leads to eutrophication. The final cause of oxygen depletion in the pond is
Aevaporation of dissolved oxygen by heat of fertilisers
Bdirect reaction of nitrate with dissolved oxygen
Caerobic decay of dead algae by bacteria
Dprecipitation of oxygen as phosphate
Answer: C
Nutrients cause an algal bloom. When the algae die, aerobic bacteria use dissolved oxygen to decompose them, so oxygen falls and fish die. Nitrate and phosphate do not react with oxygen directly.