Which of the following statements is true with regard to light reaction of photosynthetic mechanism in plants

Options

A. Chlorophyll a occurs with peak absorption at 680 nm in PS I and 700 nm in PS II
B. Mg and Na are associated with photolysis of `H_(2)O`
C. `O_(2)` is evolved during cyclic photophosphorylation
D. PS I and PS II are both involved in noncyclic photophosphorylation

Answer

To determine which statement is true regarding the light reaction of photosynthesis in plants, we need to analyze the statements provided. Here’s a step-by-step breakdown:

### Step 1: Understand the Components of Light Reactions
The light reactions of photosynthesis occur in the thylakoid membranes of chloroplasts and involve two main photosystems: Photosystem I (PS I) and Photosystem II (PS II).

### Step 2: Analyze Each Statement
1. **Statement about Chlorophyll A Absorption Peaks**:
- PS I has an absorption peak at 700 nm (P700), and PS II has an absorption peak at 680 nm (P680). The statement claiming that chlorophyll A in PS I has an absorption peak at 680 nm is incorrect.

2. **Statement about Photolysis of Water**:
- The photolysis of water involves the splitting of water molecules to release oxygen, protons, and electrons. This process requires manganese and chloride ions, not sodium and magnesium. Thus, this statement is also incorrect.

3. **Statement about Oxygen Evolution during Cyclic Photophosphorylation**:
- Cyclic photophosphorylation occurs only in PS I and does not involve the photolysis of water, meaning no oxygen is released. Therefore, this statement is incorrect.

4. **Statement about Non-Cyclic Photophosphorylation**:
- Non-cyclic photophosphorylation involves both PS I and PS II. In this process, PS II captures light energy first, leading to the splitting of water and the release of oxygen, followed by the transfer of electrons to PS I. This statement is correct.

### Conclusion
The correct statement regarding the light reaction of photosynthesis in plants is that **PS I and PS II are both involved in non-cyclic photophosphorylation**.

### Final Answer
The correct statement is: **PS I and PS II are both involved in non-cyclic photophosphorylation.**

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