Linear relationship exists between incident light and rate of ` CO_(2)` fixation at/in.

Options

A. High light intensity
B. Low light intensity
C. Dense forests
D. More than one option is correct

Answer

### Step-by-Step Solution:

1. **Understanding CO2 Fixation**: CO2 fixation is a crucial part of the photosynthesis process, specifically occurring during the dark reactions (Calvin cycle) where carbon dioxide is converted into glucose.

2. **Identifying the Relationship**: The question asks about the relationship between incident light and the rate of CO2 fixation. This relationship can be visualized by plotting a graph with incident light intensity on the x-axis and the rate of CO2 fixation on the y-axis.

3. **Low Light Intensity**: At low light intensities, there is a direct and linear relationship between the amount of light available and the rate of CO2 fixation. This means as light intensity increases, the rate of CO2 fixation also increases proportionally.

4. **High Light Intensity Effects**: When light intensity becomes high, the situation changes. High light intensity can lead to photo-oxidation of chlorophyll. This process can damage the chlorophyll molecules, reducing their efficiency in capturing light energy, and consequently, the rate of photosynthesis may decrease.

5. **Stomatal Closure**: To mitigate the risk of photo-oxidation at high light intensities, plants may close their stomata. This closure limits the intake of CO2, further decreasing the rate of CO2 fixation.

6. **Conclusion**: Therefore, the linear relationship between incident light and CO2 fixation is primarily observed at low light intensities. In dense forests, where light is limited, an increase in light intensity can enhance the rate of photosynthesis, supporting the idea that more than one condition can exhibit this linear relationship.

7. **Final Answer**: The answer to the question is that a linear relationship exists between incident light and the rate of CO2 fixation primarily at low light intensities.