Which one of the following is an indirect measure of the organic matter present in water?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → BOD
Option (1) pH level — Incorrect. pH tells how acidic or basic the water is, not how much organic matter it holds.
Option (2) Nitrogen content — Incorrect. It measures one nutrient, which may come from fertilisers as much as from organic matter.
Option (3) Turbidity — Incorrect. Turbidity is how cloudy the water is; clay and silt make water turbid too.
Option (4) BOD — Correct. BOD (biochemical oxygen demand) is the oxygen microbes would use to break down the organic matter in the water. More organic matter means more oxygen used, so BOD measures the organic matter indirectly.
NCERT Extract:
Microbes in Sewage Treatment – …
