Correct Answer - Option 1 : 6.7 ml
Concept:
BOD = BOD consumed × dilution factor
Dilution factor = volume of diluted sample/volume of undiluted sample
Calculation:
Given that, BOD of wastewater sample = 180 mg/l
BOD consumed = 4 mg/l
Volume of diluted sample = 300 ml
Let the volume of undiluted sample is X ml.
180 = 4 × (300/X)
⇒ X = 6.67 ml