question_answer 33)

  Which of the following conditions shows the polluted environment? (a) pH of rain water is 5.6                                              (b) Amount of \[C{{O}_{2}}\] in the atmosphere is 0.03% (c) Biochemical oxygen demand 10 ppm                                (d) Eutrophication

Answer:

  (c, d) Clean water has BOD value less than 5 ppm. The BOD value more than 5 ppm indicates the polluted water. The excessive growth of algae and aquatic plants due to presence of plant nutrients is called eutrophication. The decomposition of these aquatic plants utilise the dissolved oxygen which proves fatal for aquatic animals.