Liberation of `H_(2)S`/foul smell in water of tanks, ponds, etc is due to

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the liberation of hydrogen sulfide (H₂S) or foul smell in the water of tanks and ponds. We need to identify the cause of this phenomenon.

2. **Identifying Key Terms**: The key terms here are "liberation of H₂S" and "foul smell." We need to focus on what conditions lead to the production of these compounds in aquatic environments.

3. **Analyzing the Options**:
- **Option A: Anaerobiosis** - This refers to life in the absence of oxygen.
- **Option B: Aerobiosis** - This refers to life in the presence of oxygen.
- **Option C: Haemophytes** - These are plants that grow in sandy or desert conditions.
- **Option D: Biological Magnification** - This is the increase in concentration of substances in the tissues of organisms.

4. **Evaluating Each Option**:
- **Anaerobiosis**: In the absence of oxygen, certain bacteria decompose organic matter, leading to the production of H₂S, which causes a foul smell.
- **Aerobiosis**: This condition does not lead to foul smells, as oxygen is present, allowing for complete decomposition without producing H₂S.
- **Haemophytes**: These organisms are not related to the production of H₂S in water bodies.
- **Biological Magnification**: This process is unrelated to the foul smell or H₂S liberation in water.

5. **Conclusion**: The correct answer is **Option A: Anaerobiosis**. The foul smell and liberation of H₂S in tanks and ponds occur due to anaerobic conditions where bacteria break down organic matter in the absence of oxygen.