A) X-Carbon dioxide, Y-Nitrogen compounds
B) X-Nitrogen compounds; Y-Carbon dioxide
C) X-Nitrogen compounds; Y-Oxygen
D) X-Oxygen; Y-Nitrogen compounds
Correct Answer: D
Solution :
Presence of nitrates (Y) in polluted water at a point where sewage is added, provides a lot of nutrients to the algae present in the river. As a result, excessive growth of algae occurs which is called algal bloom. When this algae die, the aerobic decomposers start decomposing it, consuming rapidly the dissolved oxygen (X) of the water. But as the distance of stream from the point where sewage was added, increases, the concentration of nitrates in the water starts decreasing and concentration of dissolved oxygen starts increasing.
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