Bioindicator of `SO_(2)` pollution

Options

A. Pseudomonas putida
B. Lichens
C. Escherichia coli
D. Corals

Answer

### Step-by-Step Solution:

1. **Understanding Bioindicators**:
- A bioindicator is a biological organism that can indicate the level of pollution in its environment. It reflects the health of the ecosystem based on its presence or absence.

2. **Identifying the Organisms**:
- The question provides four options: Pseudomonas putida, lichens, H.C.D.C. coli, and corals. We need to determine which of these is a bioindicator specifically for SO2 (sulfur dioxide) pollution.

3. **Analyzing Lichens**:
- Lichens are a symbiotic association between algae and fungi. They are sensitive to air quality and can absorb nutrients from the air.

4. **Lichens and Air Pollution**:
- When the air is polluted, particularly with sulfur dioxide, the number of lichens decreases. This makes them a reliable bioindicator for air quality and specifically for SO2 pollution.

5. **Evaluating Other Options**:
- Pseudomonas putida, H.C.D.C. coli, and corals do not specifically indicate levels of SO2 pollution. They may respond to other environmental factors but are not reliable indicators for sulfur dioxide.

6. **Conclusion**:
- Based on the analysis, the correct answer is that lichens are the bioindicator for SO2 pollution.

### Final Answer:
**Lichens** are the bioindicator of SO2 pollution.

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