BOD values of three water samples A, B and C were recorded as 20 mg/L, 10 mg/L and 50 mg/L. Which of the sample is/are the most polluted?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → C
The higher the BOD, the more organic matter and so the more polluted the water. Sample C has the highest BOD (50 mg/L).
Option (4) C — Correct. BOD measures the oxygen used by microbes to break down organic matter in a litre of water. The higher the BOD, the more polluted the water, so sample C, with the highest BOD (50 mg/L), is the most polluted.
NCERT Extract:
Microbes in Sewage Treatment – “… The BOD test measures the rate of uptake of oxygen by micro-organisms in a sample of water and thus, indirectly, BOD is a measure of the organic matter present in the water. The greater the BOD of waste water, more is its polluting potential.”