Decreasing dissolved oxygen (DO) level in a water body: Choose the correct answer from the options given below:

1.Severely threatens aquatic life

2.Is mainly caused by oxygen-demanding wastes

3.Indicates the presence of biodegradable organic substances

4.Causes undesired taste and colour

5.Makes it non-drinkable to human beings

A1, 2, 3, 4 Only ✓ Correct

B2, 3, 4, 5 only

C1, 3, 4, 5 only

D1, 2, 4, 5 only

Correct answer: (A) 1, 2, 3, 4 Only

Explanation

Falling dissolved oxygen severely threatens aquatic life, is mainly caused by oxygen demanding wastes, signals biodegradable organic matter, and brings undesired taste and colour.

Statement 1 is right because fish and other aquatic animals suffocate as oxygen drops.

Statement 2 is right since decomposing organic waste consumes oxygen as it breaks down.

Statement 3 is right because such biodegradable load is exactly what drives the oxygen demand.

Statement 4 is right as the resulting decay produces off tastes and discolouration in the water.

Statement 5 is wrong because low dissolved oxygen does not by itself make water unfit for humans to drink.

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