question_answer 24)

  Biochemical Oxygen Demand (BOD) is a measure of organic material present in water. BOD value less than 5 ppm indicates a water sample to be : (a) rich in dissolved oxygen                                         (b) poor in dissolved oxygen (c) highly polluted                                                            (d) not suitable for aquated life

Answer:

  (a) The total amount of oxygen consumed by micro-organisms (bacteria) in decomposing organic matter present in certain volume of a sample of water is called Biochemical Oxygen Demand (BOD) of the water. Water considered to be pure if it has BOD less than 5 ppm whereas highly polluted water has BOD more than 17 ppm. Thus, the water having BOD less than 5 ppm is rich in dissolved oxygen.