Which of the following uses light as energy source ?

Options

A. Rhodopseudomonas
B. Nitrococcus
C. Nitrosomonas
D. Clostridium

Answer

To solve the question "Which of the following uses light as an energy source?" we need to analyze the options provided: Rhodosudomonas, Nitrococcus, Nitrosomonas, and Clostridium.

### Step-by-Step Solution:

1. **Identify the Organisms**: We have four organisms to consider:
- Rhodosudomonas
- Nitrococcus
- Nitrosomonas
- Clostridium

2. **Understand the Functionality of Each Organism**:
- **Rhodosudomonas**: This is known as a purple non-sulfur bacterium. It is classified as a phototrophic organism, meaning it can use light as an energy source for photosynthesis. It converts sunlight energy and atmospheric carbon dioxide into biomass.
- **Nitrococcus**: This bacterium is involved in the nitrification process. It oxidizes ammonia but does not use light as an energy source.
- **Nitrosomonas**: Similar to Nitrococcus, Nitrosomonas is also an ammonia-oxidizing bacterium that participates in nitrification and does not utilize light for energy.
- **Clostridium**: This is a gram-negative bacterium that is primarily known as a pathogen. It does not use light as an energy source.

3. **Determine the Correct Answer**: Among the options, only Rhodosudomonas is capable of using light as an energy source. It is specifically noted for its ability to perform photosynthesis by utilizing light.

4. **Conclusion**: Therefore, the organism that uses light as an energy source is **Rhodosudomonas**.

### Final Answer:
**Rhodosudomonas** uses light as an energy source.