MCQ on BOD and COD | Biochemical Oxygen Demand and Chemical Oxygen Demand | Environmental Science MCQ

1. When huge amount of sewage is dumped in a river, the BOD will be

a) decrease

b) increase

c) remain unchanged

d) none of these

 

2. BOD values are always less than

a) DO value

b) MPN value

c) SPC value

d) COD value

3.The optimum DO in natural water is---

a) 3-5 ppm

b) 4-6 ppm

c) 5-7ppm

d) 6-8ppm

 

4. Very low BOD level of a water body indicates that the water is ---

a) less polluted

b) highly polluted

c) contain more organic matter

d) rich in heavy metals

5. If the depletion of oxygen is found to be 2mg/l after incubating 3ml of sewage diluted to 300 ml, at 20ºC  for 5 days, then the BOD₅ of the sewage would be:

a) 100mg/l

b) 200mg/l

c) 300mg/l

d) None of these

 

6. As per the Central Pollution Control Board of India, Biological Oxygen Demand (BOD) of treated sewage should be 

a) less than 35 mg/l

b) less than 25 mg/l

c) less than 20 mg/l

d) less than 10 mg/l

 

7. While testing for COD of sewage, organic matter is oxidised by K₂Cr₂O₇

a) HCl

b) H₂SO₄

c) HNO₃

d) None of these

8. High COD to BOD ratio of an organic pollutant represents:

a) High biodegradability of the pollutant 

b) Low biodegradability of the pollutant 

c) Presence of free oxygen for aerobic decomposition

d) Presence of toxic material in the pollutant 

 

9. Standard 5-day BOD at 20ºC, when compared to ultimate BOD is about:

a) 58%

b) 68%

c) 98%

d)None of these

Answer:

1.  b) increase

2. d) COD value

3. b) 4-6 ppm

4. a) less polluted

5. b) 200mg/l

6. d) less than 10 mg/l

7.  b) H₂SO₄

8. b) Low biodegradability of the pollutant

9. b) 68%