Foul smell in the water of tanks, ponds etc. is due to

Options

A. Anaerobiosis
B. Acrobiosis
C. Biological magnification
D. Psammophytes

Answer

To answer the question regarding the foul smell in the water of tanks, ponds, etc., we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Problem**: The question asks about the cause of foul smell in water bodies like tanks and ponds.

2. **Identifying the Process**: The foul smell is primarily due to a process known as **anaerobic decomposition**. This occurs when organic matter in the water decomposes in the absence of oxygen.

3. **Role of Oxygen**: In normal conditions, aerobic bacteria decompose organic matter using oxygen, resulting in less odorous byproducts. However, when oxygen is absent (anaerobic conditions), different bacteria that thrive without oxygen take over.

4. **Decomposition of Organic Matter**: The anaerobic bacteria break down the organic matter, leading to the production of foul-smelling gases such as hydrogen sulfide (H₂S) and methane (CH₄). These gases are responsible for the unpleasant odor.

5. **Impact on Aquatic Life**: The absence of oxygen not only affects the decomposition process but also leads to the death of aquatic plants and animals, further contributing to the foul smell as their decay adds to the organic matter in the water.

6. **Conclusion**: Therefore, the foul smell in the water of tanks, ponds, etc., is primarily due to anaerobic decomposition caused by the absence of oxygen.

### Final Answer:
The foul smell in the water of tanks, ponds, etc., is due to anaerobic decomposition of organic matter, which occurs in the absence of oxygen.

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