The measured BOD values for four different water samples (A - D) are as follows: A = 3 ppm; B = 18 ppm; C = 21 ppm; D = 4 ppm. The water samples which can be called as highly polluted with organic wastes, are

We need to identify the water samples that are highly polluted with organic wastes based on their BOD values. The BOD values for the samples are A = 3 ppm, B = 18 ppm, C = 21 ppm, and D = 4 ppm.

Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen needed by aerobic organisms to break down organic material in water. A higher BOD indicates more organic pollution.

Water with BOD < 5 ppm is considered clean, while water with BOD > 17 ppm is considered highly polluted.

A = 3 ppm — Clean water
B = 18 ppm — Highly polluted (BOD > 17 ppm)
C = 21 ppm — Highly polluted (BOD > 17 ppm)
D = 4 ppm — Clean water

The highly polluted samples are B and C.

The correct answer is Option C: B & C.