Indicators for atmospheric pollution by `SO_(2)` are

Options

A. lichens like Usnea
B. grassland like Deschampsia
C. moss like Sphagnum
D. climbers like Cucurbita

Answer

To determine the indicators for atmospheric pollution by sulfur dioxide (SO₂), we can analyze the given options based on their characteristics and sensitivity to SO₂.

### Step-by-Step Solution:

1. **Understanding SO₂ and its Effects**:
- Sulfur dioxide (SO₂) is a significant air pollutant that can lead to the formation of acid rain when it reacts with water and air. Acid rain can be detrimental to the environment, affecting plants, animals, and human health.

2. **Identifying Bio-indicators**:
- Bio-indicators are organisms that reflect the health of an environment or ecosystem. They can indicate the presence of pollutants like SO₂ by showing sensitivity to changes in air quality.

3. **Evaluating the Options**:
- **Option A: Lichens (like Usnea)**: Lichens are symbiotic associations of algae and fungi. They absorb nutrients directly from the atmosphere and are highly sensitive to air pollution, particularly SO₂. Their lack of roots makes them particularly vulnerable to airborne pollutants.
- **Option B: Grasslands (like Dystampsia)**: Grasslands are not specific indicators of SO₂ pollution. While they can be affected by pollution, they do not serve as reliable bio-indicators for SO₂.
- **Option C: Moss (like Sphagnum)**: Mosses can indicate some levels of environmental health, but they are not as sensitive to SO₂ as lichens are.
- **Option D: Climbers (like Cucurbita)**: Climbers, such as Cucurbita, are not known to be effective bio-indicators for atmospheric pollution by SO₂.

4. **Conclusion**:
- Among the options provided, **lichens (like Usnea)** are the best indicators for atmospheric pollution by sulfur dioxide due to their high sensitivity and ability to absorb pollutants directly from the air.

### Final Answer:
The correct indicator for atmospheric pollution by SO₂ is **lichens like Usnea (Option A)**.

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