To determine the truth of the statements provided in the question, we will analyze each statement step by step.
### Step 1: Analyze Statement A
**Statement A:** The portion of the spectrum between 500 nm and 800 nm is also referred to as photosynthetically active radiation (PAR).
- **Analysis:** Photosynthetically Active Radiation (PAR) is typically defined as the light spectrum that plants use for photosynthesis, which ranges from approximately 400 nm to 700 nm. The range of 500 nm to 800 nm includes some wavelengths that are not considered active for photosynthesis. Specifically, the effective range for PAR is generally accepted to be from about 400 nm to 700 nm, with the most effective wavelengths being around 600 nm to 700 nm (red light). Therefore, this statement is **false**.
### Step 2: Analyze Statement B
**Statement B:** Magnesium, calcium, and chloride ions play prominent roles in the photolysis of water.
- **Analysis:** In the process of photolysis of water, which occurs during photosynthesis, the primary element involved is manganese (Mn), which is part of the oxygen-evolving complex of Photosystem II. While magnesium (Mg) is essential for chlorophyll and overall plant health, and calcium (Ca) plays various roles in cellular processes, they do not directly participate in the photolysis of water. Chloride ions are also not directly involved in this process. Therefore, this statement is **false**.
### Step 3: Analyze Statement C
**Statement C:** In cyclic photophosphorylation, oxygen is not released (as there is no photolysis of water) and NADPH is also not produced.
- **Analysis:** Cyclic photophosphorylation occurs when there is a scarcity of NADP+. In this process, electrons are cycled back to Photosystem I, leading to the production of ATP without the production of NADPH. Since photolysis of water does not occur in cyclic photophosphorylation, oxygen is not released. Therefore, this statement is **true**.
### Conclusion
- **Statement A:** False
- **Statement B:** False
- **Statement C:** True
Thus, the correct answer is that **only Statement C is true**.
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