Which one is incorrect statement regarding eutrophication?

Options

A. In eutrophication dissolved `O_(2)` concentration decreases
B. Eutrophication occurs due to excess `PO_(4)^(3-)` present in `H_(2)O`
C. Algae reduces dissovled `O_(2)` in `H_(2)O`
D. Main cause of eutrophication is presence of `NO_(3)^(-)`

Answer

To determine which statement regarding eutrophication is incorrect, let's analyze each statement step by step.

### Step 1: Understand Eutrophication
Eutrophication is a process where water bodies receive excess nutrients, primarily phosphorus and nitrogen, leading to excessive growth of algae. This process can result in decreased oxygen levels in the water, harming aquatic life.

### Step 2: Analyze Each Statement
1. **In eutrophication, dissolved O2 concentration decreases.**
- This statement is **correct**. As algae grow and decompose, the oxygen in the water is consumed, leading to lower dissolved oxygen levels.

2. **Eutrophication occurs due to the excess phosphate ions present in the water.**
- This statement is **correct**. Eutrophication is often triggered by high levels of phosphorus, which can come from fertilizers and other sources.

3. **Algae reduces dissolved O2 in the water.**
- This statement is **incorrect** in its wording. While algae growth can lead to reduced oxygen levels due to decomposition, algae themselves do not reduce oxygen; instead, they produce oxygen during photosynthesis. However, the decomposition of algae consumes oxygen, which is where the confusion may arise.

4. **Main cause of eutrophication is the presence of NO3- ions.**
- This statement is **incorrect**. While nitrates (NO3-) can contribute to eutrophication, the primary cause is typically the presence of phosphate ions (PO4^3-).

### Conclusion
Based on the analysis, the statement that is incorrect regarding eutrophication is: **"Main cause of eutrophication is presence of NO3- ions."**

### Final Answer
The incorrect statement regarding eutrophication is: **"Main cause of eutrophication is presence of NO3- ions."**

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