The oxygen evolved during photosynthesis comes from water molecules . Which one of the following pairs of elements is involved in this reaction ?
(a) Magnesium and Chlorine
(b) Manganese and Chlorine
(c) Manganese and Potassium
(d) Magnesium and Molybdenum

Options

A. Magnesium and Chlorine
B. Manganese and Chlorine
C. Manganese and Potassium
D. Magnesium and Molybdenum

Answer

To solve the question regarding which pair of elements is involved in the reaction where oxygen is evolved during photosynthesis from water molecules, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Photosynthesis**:
- Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, using carbon dioxide and water. Oxygen is released as a by-product.

2. **Identifying the Source of Oxygen**:
- The question states that the oxygen evolved during photosynthesis comes from water molecules (H2O). This process is known as oxygenic photosynthesis.

3. **Role of Water in Photosynthesis**:
- In oxygenic photosynthesis, water acts as the electron donor. During the light-dependent reactions, water molecules are split into oxygen, protons, and electrons.

4. **Location of Water Splitting**:
- The splitting of water occurs at Photosystem II (PS II) in the thylakoid membranes of chloroplasts. This process is facilitated by a complex known as the oxygen-evolving complex (OEC).

5. **Elements Involved in Water Splitting**:
- The water-splitting complex requires specific elements to function. The key elements involved in this process are manganese (Mn) and chlorine (Cl). Manganese plays a crucial role in the catalytic activity of the OEC, while chlorine is also associated with the process.

6. **Evaluating the Options**:
- Now, let's evaluate the given options:
- (a) Magnesium and Chlorine
- (b) Manganese and Chlorine
- (c) Manganese and Potassium
- (d) Magnesium and Molybdenum
- From our understanding, the correct pair of elements that are involved in the reaction where oxygen is evolved from water is **Manganese and Chlorine**.

7. **Conclusion**:
- Therefore, the correct answer is **(b) Manganese and Chlorine**.