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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ev165

Select the correct statements about sewage and other sources of water pollution.

  1. ARun-off of fertilisers lowers the nitrate content of lake water
  2. BSewage can carry pathogens such as Vibrio cholerae
  3. CIndustrial effluents contain only biodegradable matter, so BOD alone describes them fully
  4. DAn oil slick on water limits the exchange of oxygen between air and water

Answer: B, D

Sewage contains pathogenic bacteria, viruses and protozoa, and an oil film hinders oxygen transfer. Fertiliser run-off raises, not lowers, nitrate. Effluents often contain non-biodegradable and inorganic pollutants that BOD does not capture.
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