Water sample is reported to be highly polluted if BOD (Biological Oxygen Demand) value of sample becomes

BOD (Biological Oxygen Demand) is the amount of dissolved oxygen required by aerobic micro-organisms to decompose the organic matter present in a water sample at $$25^{\circ} \text{C}$$ over a period of 5 days.

It is used as an index of organic pollution:

• Pure water or water that is safe for domestic use has a BOD of $$\lt 5$$ ppm (mg $$\text{O}_2$$ per litre).
• Moderately polluted water shows BOD values between $$5$$ and $$17$$ ppm.
• If the BOD exceeds $$17$$ ppm, the water is classified as highly polluted because such a high oxygen demand indicates a large concentration of biodegradable organic wastes.

Therefore, a water sample is reported to be highly polluted when its BOD value is more than $$17$$ ppm.

Option A which is: more than $$17$$ ppm