The correct answer is option 'C', which states that the reaction center of photosystem II absorbs red light with a wavelength of 680nm. In order to understand why this is the correct answer, let's break it down and discuss the details.

Importance of Photosystem II:
Photosystem II (PSII) is one of the two photosystems found in the thylakoid membrane of chloroplasts in plant cells. It plays a crucial role in the process of photosynthesis, specifically in the light-dependent reactions.

Structure of Photosystem II:
Photosystem II consists of various pigment molecules, including chlorophyll a, chlorophyll b, and carotenoids, which are arranged in a specific manner within the thylakoid membrane. These pigments are responsible for capturing light energy and initiating the process of photosynthesis.

Absorption Spectrum of Photosystem II:
The absorption spectrum of a pigment shows the range of wavelengths of light that it can absorb. In the case of photosystem II, the absorption spectrum shows that the reaction center absorbs light with a peak wavelength of 680nm, which falls within the red region of the visible light spectrum.

Explanation of the Correct Answer:
The correct answer, option 'C', states that the reaction center of photosystem II absorbs red light with a wavelength of 680nm. This is based on experimental evidence and the absorption spectrum of photosystem II. The reaction center pigments in photosystem II have a primary pigment called P680, which is a form of chlorophyll a. P680 absorbs red light most efficiently, allowing the plant to harness the maximum amount of energy from this specific wavelength of light.

The Absorption of Other Wavelengths:
While photosystem II primarily absorbs red light at 680nm, it also absorbs light at slightly shorter wavelengths, including blue light (~440-450nm). However, the absorption at 680nm is the most significant, hence the correct answer choice 'C' identifies red light as the main wavelength absorbed by the reaction center of photosystem II.

Conclusion:
In summary, the reaction center of photosystem II absorbs red light with a wavelength of 680nm. This absorption allows plants to capture light energy and initiate the process of photosynthesis. Understanding the absorption spectrum of photosystem II is essential in comprehending the light-dependent reactions and the role of photosystems in converting light energy into chemical energy.