For the survival of fish in a river stream, the minimum dissolved oxygen is prescribed________________?

Related Mcqs:

1. If a 2% solution of sewage sample is incubated for 5 days at 20°C and the dissolved oxygen depletion was found to be 8 mg/l. The BOD of the sewage is_________________?

   A. 100 mg/l
   B. 200 mg/l
   C. 300 mg/l
   D. 400 mg/l

2. Assertion A. : Discharging the effluents from the oxidation ponds just up stream of lakes or reservoirs is undesirable. Reason (R) : The discharged algae get settled in the reservoirs and cause anaerobic decomposition and other water qualities_________________?

   A. Both A and R are true and R is the correct explanation of A
   B. Both A and R are true but R is not a correct explanation of A
   C. A is true but R is false
   D. A is false but R is true

3. If the depletion of oxygen is found to be 5 ppm after incubating a 2.5% solution of sewage sample for 5 days at 21°C, B.O.D. of the sewage is_____________________?

   A. 50 ppm
   B. 100 ppm
   C. 150 ppm
   D. 200 ppm

4. To test chemical oxygen demand (C.O.D.) of sewage, organic matter is oxidised by potassium dichromate in the presence of_______________?

   A. Hydrochloric acid
   B. Sulphuric acid
   C. Nitric acid
   D. Citric acid

5. If the depletion of oxygen is found to be 2.5 mg/litre after incubating 2.5 ml of sewage diluted to 250 ml for 5 days at 20°C, B.O.D. of the sewage is_________________?

   A. 50 mg/l
   B. 100 mg/l
   C. 150 mg/l
   D. 250 mg/l

6. If 2% solution of a sewage sample is incubated for 5 days at 20°C and depletion of oxygen was found to be 5 ppm, B.O.D. of the sewage is____________________?

   A. 200 ppm
   B. 225 ppm
   C. 250 ppm
   D. None of these

7. Bio-chemical oxygen demand (BOD) for the first 20 days in generally referred to_______________?

   A. Initial demand
   B. First stage demand
   C. Carbonaceous demand
   D. All of these

8. 5 days-biochemical oxygen demand (BOD5) is taken at a temperature of_________________?

   A. 0°C
   B. 15°C
   C. 20°C
   D. 25°C

9. The amount of oxygen consumed by the aerobic bacterias which cause the aerobic biological decomposition of sewage, is known_________________?

   A. Bio-Chemical Oxygen Demand (B.O.D.)
   B. Dissolved Oxygen (D.O.)
   C. Chemical Oxygen Demand (C.O.D.)
   D. None of these

10. The factor responsible for purification of sewage in river is________________?

    A. Hydrology
    B. Dissolved oxygen in water
    C. Temperature
    D. All the above