Which of the following is absent in polluted water?

Options

A. Hydrilla
B. Water hyacinth
C. Larva of stone fly
D. Blue green algae

Answer

**Step-by-Step Solution:**

1. **Identify the Options**: The question presents four options:
- a) Hydrilla
- b) Water Hyacinth
- c) Larva of a Stonefly
- d) Blue Green Algae

2. **Understand the Nature of Polluted Water**: Polluted water typically has a high concentration of toxins, low oxygen levels, and a lack of biodiversity. Many aquatic organisms cannot survive in such conditions.

3. **Analyze Each Option**:
- **Hydrilla**: This is a type of aquatic plant that can thrive in various water conditions, including polluted waters.
- **Water Hyacinth**: This is another aquatic plant known for its ability to grow in polluted water, often thriving in nutrient-rich environments.
- **Larva of a Stonefly**: Stonefly larvae are sensitive to pollution. They require well-aerated, non-polluted water to survive. The presence of pollutants can lead to the elimination of their food sources, such as lichens and algae.
- **Blue Green Algae**: These can thrive in polluted waters, especially in nutrient-rich environments, often leading to algal blooms.

4. **Determine the Correct Answer**: Based on the analysis, the larva of a stonefly is the only organism from the options that is absent in polluted water due to its sensitivity to pollution and the requirement for clean, well-oxygenated water.

5. **Conclusion**: The correct answer to the question is **c) Larva of a Stonefly**.

---