In which of the following all listed genera belong to the same class of algae

Options

A. Chara, Fucus, Polysiphonia
B. Volvox, Spirogyra, Chlamydomonas
C. Porphyra, Ectocarpus, Ulothrix
D. Sargassum, Laminaria, Gracilaria.

Answer

To solve the question of which of the listed genera belong to the same class of algae, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Identify the Genera in Each Option**:
- **Option A**: Chara, Fucus, Polysiphonia
- **Option B**: Volvox, Spirogyra, Chlamydomonas
- **Option C**: Porphyra, Ectocarpus, Eulothrix
- **Option D**: Sargassum, Laminaria, Gracilaria

2. **Classify Each Genus**:
- **Chara**: Belongs to the class Chlorophyceae (Green Algae).
- **Fucus**: Belongs to the class Phaeophyceae (Brown Algae).
- **Polysiphonia**: Belongs to the class Rhodophyceae (Red Algae).

Since Chara, Fucus, and Polysiphonia belong to different classes, **Option A is incorrect**.

3. **Analyze Option B**:
- **Volvox**: Belongs to the class Chlorophyceae (Green Algae).
- **Spirogyra**: Belongs to the class Chlorophyceae (Green Algae).
- **Chlamydomonas**: Belongs to the class Chlorophyceae (Green Algae).

All three genera belong to the same class (Chlorophyceae), so **Option B is correct**.

4. **Analyze Option C**:
- **Porphyra**: Belongs to the class Rhodophyceae (Red Algae).
- **Ectocarpus**: Belongs to the class Phaeophyceae (Brown Algae).
- **Eulothrix**: Belongs to the class Chlorophyceae (Green Algae).

Since these three belong to different classes, **Option C is incorrect**.

5. **Analyze Option D**:
- **Sargassum**: Belongs to the class Phaeophyceae (Brown Algae).
- **Laminaria**: Belongs to the class Phaeophyceae (Brown Algae).
- **Gracilaria**: Belongs to the class Rhodophyceae (Red Algae).

Since Sargassum and Laminaria are both brown algae but Gracilaria is a red alga, **Option D is incorrect**.

### Conclusion:
The only option where all listed genera belong to the same class of algae is **Option B (Volvox, Spirogyra, Chlamydomonas)**, which all belong to the class Chlorophyceae.