Decline in quantum yield was noticed by Emerson at a wavelength of

Options

A. 400-450 nm
B. 600-650 nm
C. 650-680 nm
D. more than 680 nm.

Answer

**Step-by-Step Solution:**

1. **Understanding Quantum Yield**: Quantum yield refers to the amount of light (or quanta) required for the release of one molecule of oxygen during photosynthesis. It is an important measure of the efficiency of photosynthesis.

2. **Emerson's Observation**: The decline in quantum yield was observed by the scientist Emerson. This phenomenon is known as the "red drop effect."

3. **Red Drop Effect**: The red drop effect indicates that there is a decline in quantum yield when light wavelengths exceed a certain threshold. Specifically, this decline is noted when wavelengths go beyond 680 nanometers.

4. **Analyzing the Options**: The question provides four options regarding the wavelength at which the decline in quantum yield was observed:
- 400 to 450 nanometers
- 600 to 650 nanometers
- 650 to 680 nanometers
- More than 680 nanometers

5. **Identifying the Correct Answer**: Based on Emerson's findings, the decline in quantum yield occurs when the light wavelength exceeds 680 nanometers. Therefore, the correct answer is "more than 680 nanometers."

**Final Answer**: More than 680 nanometers.

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