Select the incorrect option w.r.t. blue green algae.

Options

A. It adds organic matter to the soil
B. It increases soil fertility
C. It reduces alkalinity of soil
D. It is restricted to terrestrial environment only

Answer

To solve the question regarding the incorrect option with respect to blue-green algae (cyanobacteria), let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Blue-Green Algae**:
- Blue-green algae, also known as cyanobacteria, are photosynthetic organisms found in various environments, including aquatic and terrestrial ecosystems.

2. **Option Analysis**:
- **Option 1**: "It adds organic matter into the soil."
- **Explanation**: Cyanobacteria contribute organic matter to the soil through their metabolic processes, especially nitrogen fixation. This option is **correct**.

- **Option 2**: "Increase soil fertility."
- **Explanation**: By adding organic matter and fixing nitrogen, cyanobacteria enhance soil fertility. This option is **correct**.

- **Option 3**: "Reduce alkalinity."
- **Explanation**: Cyanobacteria can help reduce soil alkalinity by increasing the organic matter content and influencing the pH levels. This option is **correct**.

- **Option 4**: "Restricted to terrestrial environment only."
- **Explanation**: This statement is **incorrect** because cyanobacteria are found in both terrestrial (land) and aquatic (water) environments. They are not restricted to just terrestrial habitats.

3. **Conclusion**:
- The incorrect option regarding blue-green algae is **Option 4**: "Restricted to terrestrial environment only."

### Final Answer:
The incorrect option with respect to blue-green algae is **Option 4**.