Question

Identify the correct statements about Eutrophication
• [I.] It takes place in air
• [II.] It is due to excess oxygen in water
• [III.] It occurs in water
• [IV.] It leads to the destruction of aquatic life The correct answer is

• A. I, II, III, IV
• B. I, III only
• C. III, IV only
• D. I, II only \bigskip

Hint:

Eutrophication: \[ \text{Excess Nutrients} \rightarrow \text{Algal Bloom} \rightarrow \text{Oxygen Depletion} \rightarrow \text{Death of Aquatic Organisms} \] Remember: It is caused by nitrates and phosphates, not by excess oxygen.

Answer 1

The Correct Option is C

Concept: Eutrophication is the enrichment of water bodies with nutrients such as nitrates and phosphates. These nutrients promote excessive growth of algae and aquatic plants. As algae die and decompose, dissolved oxygen in water decreases drastically, causing harm to aquatic organisms.

Step 1: Examine Statement I.
Statement I says eutrophication takes place in air. Eutrophication is a phenomenon associated with lakes, ponds, reservoirs and rivers. Hence it occurs in water and not in air. Therefore Statement I is incorrect.

Step 2: Examine Statement II.
The process is not caused by excess oxygen. Instead, it is caused by excess nutrients such as nitrates and phosphates entering water bodies through sewage and fertilizers. Moreover, eutrophication eventually reduces dissolved oxygen concentration. Therefore Statement II is incorrect.

Step 3: Examine Statement III.
Eutrophication is a water pollution phenomenon. Thus Statement III is correct.

Step 4: Examine Statement IV.
Algal bloom consumes oxygen during decomposition. The depletion of oxygen causes fish kills and destruction of aquatic life. Therefore Statement IV is correct. Hence the correct statements are: \[ III \text{ and } IV \] \[ \boxed{\text{Option (C)}} \]