Disappearance of fish from water bodies usually indicates excess of `"…….."` in water

Options

A. Zn
B. Hg
C. Fluoride
D. Fe

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks what substance's excess in water bodies leads to the disappearance of fish.

2. **Identifying Water Pollution Causes**: Water pollution is a significant factor affecting aquatic life. Various pollutants, including industrial waste, sewage, and garbage, are often dumped into water bodies, leading to toxic conditions.

3. **Analyzing the Given Options**: The options provided are zinc, mercury, fluoride, and iron. We need to determine which of these is most harmful to fish.

4. **Researching Each Substance**:
- **Zinc**: While it can be harmful in high concentrations, it is not typically the primary cause of fish disappearance.
- **Mercury**: This is a well-known toxic substance that can accumulate in aquatic organisms. It converts to methyl mercury in water, which is highly toxic to fish and other aquatic life.
- **Fluoride**: Although it can be harmful, it is not commonly associated with the mass disappearance of fish.
- **Iron**: Generally, iron is not considered a major pollutant that would lead to fish death.

5. **Conclusion**: Based on the analysis, mercury is the substance that, when present in excess, leads to the disappearance of fish from water bodies due to its toxic effects and accumulation in aquatic life.

### Final Answer:
The disappearance of fish from water bodies usually indicates excess of **mercury** in water.

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