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JEE Main levelSingle correct optionDifficulty 2 of 3ev122

Following the standard NCERT treatment, a river sample is found to have a BOD of 25 ppm. It is best described as:

  1. Apolluted only by inorganic salts
  2. Bclean water
  3. Cfree of dissolved organic matter
  4. Dhighly polluted with biodegradable organic matter

Answer: D

Clean water has BOD below 5 ppm, and a BOD above 17 ppm indicates heavy pollution. A value of 25 ppm therefore means a large load of oxidisable organic matter.
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