The amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria, what is it called ?

BOD

The correct answer is Option (3)- BOD

The amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria is referred to as BOD (Biochemical Oxygen Demand).

BOD is a measure used to quantify the amount of oxygen consumed by microorganisms during the decomposition of organic matter present in water. It indicates the level of organic pollutants or biodegradable substances in water. High BOD levels suggest a higher concentration of organic matter, which, when decomposed by bacteria, consumes more oxygen, potentially leading to decreased dissolved oxygen levels in the water, which can be detrimental to aquatic life.

The sewage water is treated till the BOD is reduced. 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.