Q43. | The minimum dissolved oxygen which should always be present in water in order to save the aquatic life is : |
Q44. | The type of valve, which is provided on the suction pipe in a tube-well is : |
Q45. | The correct relation between theoretical oxygen demand (TOD),Biochemical oxygen demand (BOD) and chemical oxygen demand ?(COD) is: |
Q46. | Composting and Lagooning are the methods of : |
Q47. | Which of the following retards the self purification of stream ? |
Q48. | The primary pollution caused by incomplete combustion of organic matter is : |