Which helped in confirming that oxygen evolved in photosynthesis comes from water

Options

A. `H_(2).^(18)O`
B. `.^(14)CO^(2)`
C. `.^(15)NO_(3)`
D. `.^(3)H_(2)O`.

Answer

To answer the question, "Which helped in confirming that oxygen evolved in photosynthesis comes from water," 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, producing glucose and oxygen from carbon dioxide and water.

2. **Role of Water in Photosynthesis**:
- In the process of photosynthesis, water (H2O) acts as a source of electrons and protons. It is split into oxygen, protons, and electrons during the light-dependent reactions.

3. **Radioisotopic Technique**:
- To confirm that the oxygen released during photosynthesis comes from water, scientists used a radioisotopic technique. This involves using isotopes to trace the origin of oxygen.

4. **Use of Isotope**:
- Instead of using normal water (H2O), scientists used water that contained the heavy isotope of oxygen, known as 18O (H2^18O). This allowed them to track the oxygen atoms during the photosynthesis process.

5. **Observation**:
- After conducting experiments, it was observed that the oxygen released during photosynthesis was labeled as 18O2, indicating that the oxygen evolved indeed came from the water that contained the isotope.

6. **Conclusion**:
- The experiment demonstrated that the oxygen produced in photosynthesis is derived from water, confirming that water is the source of the oxygen released during the process.

### Final Answer:
The correct answer is the use of **H2^18O (heavy water)** in experiments, which confirmed that the oxygen evolved in photosynthesis comes from water.

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