In an experiment on `O_(2)` evolution by photosynthesising Hydrilla plant, a pinch of sodium bicarbonate is added to water. The rate of photosynthesis or `O_(2)` evolution will

Options

A. Increase
B. Decrease
C. Stop
D. Not be affected.

Answer

To solve the question regarding the effect of adding sodium bicarbonate to water in an experiment on oxygen evolution by the photosynthesizing Hydrilla plant, follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of Sodium Bicarbonate**:
- Sodium bicarbonate (NaHCO₃) when dissolved in water dissociates to release bicarbonate ions (HCO₃⁻) and sodium ions (Na⁺). Importantly, bicarbonate can further react in water to release carbon dioxide (CO₂).

2. **Recognize the Importance of Carbon Dioxide in Photosynthesis**:
- Photosynthesis is the process by which plants convert carbon dioxide and water into glucose and oxygen, using sunlight as energy. The general equation for photosynthesis is:
\[ 6CO₂ + 6H₂O \xrightarrow{light \ energy} C₆H₁₂O₆ + 6O₂ \]
- Here, CO₂ is a crucial raw material for the process.

3. **Effect of Increased Carbon Dioxide on Photosynthesis**:
- When sodium bicarbonate is added, it increases the availability of carbon dioxide in the water. This increase in CO₂ concentration provides more substrate for the photosynthesis reaction.

4. **Conclusion on Oxygen Evolution**:
- As the concentration of carbon dioxide increases, the rate of photosynthesis will also increase, leading to a higher rate of oxygen (O₂) evolution. This is because more carbon dioxide allows the plant to produce more glucose and, consequently, more oxygen as a byproduct.

5. **Final Answer**:
- Therefore, the rate of photosynthesis or O₂ evolution will **increase** when sodium bicarbonate is added to the water.