A reduction in `O_(2)` evolution occurs when light wavelength is

Options

A. More than 680 nm
B. Less than 680 nm
C. Less then 660 nm
D. 560 nm.

Answer

To solve the question regarding the reduction in oxygen evolution when light wavelength changes, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of Light in Photosynthesis**:
- Photosynthesis primarily occurs in chloroplasts where light energy is converted into chemical energy. Oxygen is produced as a byproduct during the photolysis of water, which occurs in Photosystem II.

2. **Identify Key Wavelengths**:
- The optimal wavelengths for photosynthesis, particularly for oxygen evolution, are around 680 nanometers (nm). This wavelength is crucial for the functioning of Photosystem II.

3. **Analyze the Effect of Wavelength on Photosynthesis**:
- When light wavelengths exceed 680 nm, the efficiency of photosynthesis decreases. This is because longer wavelengths (such as those greater than 680 nm) do not effectively excite the chlorophyll pigments involved in the photochemical reactions.

4. **Explain the Concept of Quantum Yield**:
- Quantum yield refers to the number of oxygen molecules produced per quantum of light absorbed. As the wavelength increases beyond the optimal range (680 nm), the quantum yield decreases, leading to reduced oxygen evolution.

5. **Introduce the Red Drop Effect**:
- The phenomenon where the efficiency of photosynthesis drops at longer wavelengths is known as the "red drop effect." This effect indicates that wavelengths longer than 680 nm are less effective in driving the photochemical reactions necessary for oxygen production.

6. **Conclusion**:
- Therefore, a reduction in oxygen evolution occurs when the light wavelength is greater than 680 nm.

### Final Answer:
The reduction in O₂ evolution occurs when the light wavelength is more than 680 nanometers.

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