127.  No treatment of the sewage is given if dilution factor is
A. less than 150
B. between 150 to 200
C. between 200 to 300
D. more than 500.

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128.  Pick up the correct statement from the following :
A. The ratio of the quantity of the diluting water to that of the sewage, is known as dilution factor
B. The automatic purification of polluted water, is known self purification phenomenon
C. The photosynthesis is carried out in the presence of sun light
D. All the above.

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129. The factor responsible for purification of sewage in river is
A. Hydrology
B. Dissolved oxy in water
C. Temperature
D. All the above.

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130.  If D.O. concentration falls down to zero in any natural drainage, it indicates the zone of
A. degradation
B. active decomposition
C. recovery
D. cleaner water

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131.  The algae dies out in the zone of
A. degradation
B. active decomposition
C. recovery
D. cleaner water.

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132.  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.

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133. As compared to fresh river water, sea water contains oxygen
A. 10% less
B. 20% less
C. 10% more
D. 20% more.

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