Air pollution indicator is

Options

A. Mycorrhiza
B. Algae
C. Fungi
D. Lichen

Answer

### Step-by-Step Solution:

1. **Identify the Concept**: The question asks for an air pollution indicator, which refers to an organism or substance that signifies the presence of air pollution.

2. **Understand the Role of Lichen**: Lichen is identified as an air pollution indicator. It is a symbiotic organism composed of two different types of organisms: algae and fungi.

3. **Explain the Symbiotic Relationship**: In this relationship, algae perform photosynthesis to produce food, while fungi provide a protective structure and absorb water and nutrients from the environment.

4. **Link to Pollution**: Lichens are sensitive to air quality. They thrive in clean air and are unable to grow in polluted areas. This sensitivity makes them excellent indicators of air pollution levels.

5. **Conclusion**: Therefore, the answer to the question is that the air pollution indicator is Lichen.

### Final Answer:
The air pollution indicator is Lichen.

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