In five-kingdom classification system, the kingdom that includes, the blue-green algae, nitrogen-fixing bacteria and methanogenic archaebacteria is

Options

A. Plantae
B. Fungi
C. Protista
D. Monera.

Explanation

To solve the question regarding the kingdom that includes blue-green algae, nitrogen-fixing bacteria, and methanogenic archaebacteria in the five-kingdom classification system, follow these steps:

### Step-by-Step Solution:

1. **Understand the Five-Kingdom Classification System**:
- The five-kingdom classification system includes Monera, Protista, Fungi, Plantae, and Animalia.
- It categorizes organisms based on their cellular organization and nutritional modes.

2. **Identify the Characteristics of the Organisms in Question**:
- Blue-green algae (also known as cyanobacteria) are photosynthetic prokaryotes.
- Nitrogen-fixing bacteria are also prokaryotic organisms that convert atmospheric nitrogen into a usable form for plants.
- Methanogenic archaebacteria are a type of archaea that produce methane as a metabolic byproduct.

3. **Determine the Cellular Organization**:
- All the mentioned organisms (blue-green algae, nitrogen-fixing bacteria, and methanogenic archaebacteria) are unicellular and lack a true nucleus, which characterizes prokaryotic cells.

4. **Identify the Correct Kingdom**:
- Since all the organisms mentioned are prokaryotes, they fall under the kingdom Monera, which includes all prokaryotic organisms.

5. **Conclusion**:
- Therefore, the kingdom that includes blue-green algae, nitrogen-fixing bacteria, and methanogenic archaebacteria is **Monera**.

### Final Answer:
The kingdom that includes blue-green algae, nitrogen-fixing bacteria, and methanogenic archaebacteria is **Monera**.