Lichens are described as indicators of

Options

A. Soil pollution
B. Air pollution
C. Water pollution
D. Agricultural productivity.

Answer

### Step-by-Step Solution:

1. **Understanding Lichens**: Lichens are symbiotic organisms composed of a fungus and a photosynthetic partner, usually algae or cyanobacteria. They are known for their ability to survive in harsh environments.

2. **Lichens as Bioindicators**: Lichens are sensitive to environmental changes, particularly air quality. They are often used as bioindicators to assess the health of an ecosystem.

3. **Sensitivity to Pollutants**: Lichens are particularly sensitive to sulfur dioxide (SO2) and other air pollutants. High concentrations of these pollutants can harm or kill lichens.

4. **Implications of Lichen Presence**: If lichens are present in an area, it typically indicates that the air quality is good, and the area is relatively free from significant air pollution. Conversely, their absence can suggest high levels of air pollution.

5. **Conclusion**: Based on the sensitivity of lichens to air quality, they are described as indicators of air pollution. Therefore, the correct answer to the question is **air pollution**.