Consider the following statements:

1.Aquatic organisms depend on dissolved oxygen, which mainly depends on temperature and sediment

2.BOD is the oxygen consumed by bacteria decomposing organic matter aerobically

3.COD is the oxygen required for chemical oxidation of total organic matter in water

AOnly statements 1 and 2 are true

BOnly statements 2 and 3 are true

COnly statements 1 and 3 are true

DAll the statements 1, 2 and 3 are true ✓ Correct

Correct answer: (D) All the statements 1, 2 and 3 are true

Explanation

Statement 1 is taken as correct, since aquatic life depends on dissolved oxygen, which itself varies mainly with temperature and related factors.

Statement 2 is correct, as biochemical oxygen demand is the oxygen used by bacteria that decompose organic matter aerobically.

Statement 3 is correct, since chemical oxygen demand is the oxygen needed to chemically oxidise the total organic matter in water.

Chemical oxygen demand is usually higher than biochemical oxygen demand for the same sample.

All three statements therefore hold true.

High organic pollution lowers dissolved oxygen and can suffocate aquatic organisms.

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