Unicellular green alga is

Options

A. Ulothrix
B. Spirogyra
C. Chlamydomonas
D. All the above.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a unicellular green alga. Unicellular organisms are those that consist of a single cell, and green algae belong to the group known as Chlorophyta.

2. **Identifying the Options**: The options provided are:
- A. Eulothrix
- B. Chlamydomonas
- C. Spirogyra
- D. All of the above

3. **Analyzing Each Option**:
- **Eulothrix**: This is a genus of green algae that is indeed unicellular and can be found in both freshwater and marine environments.
- **Chlamydomonas**: This is another genus of green algae known for being unicellular. It can also be found in both freshwater and marine environments.
- **Spirogyra**: This genus is primarily known for its filamentous structure, which is multicellular. Therefore, it does not fit the description of being unicellular.

4. **Conclusion**: Since both Eulothrix and Chlamydomonas are unicellular green algae, but Spirogyra is not, the correct answer cannot be "D. All of the above." The correct answer is actually a choice between A and B.

5. **Final Answer**: The correct unicellular green alga from the options given is **B. Chlamydomonas**.