If oxygen is labelled with `(18^@)`, which molecules will become radioactive as glycolysis, Kreb's cycle and oxidation phosphorylation are completed -

Options

A. Water
B. `CO_(2)`
C. ATP
D. `NADH_(2)`

Answer

To determine which molecules will become radioactive when oxygen is labeled with \(^{18}O\) as glycolysis, the Krebs cycle, and oxidative phosphorylation are completed, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Labeling of Oxygen**:
- The oxygen molecule is labeled with \(^{18}O\), which is a heavier isotope of oxygen compared to the more common \(^{16}O\). This means that any molecule that incorporates this \(^{18}O\) will also become radioactive.

2. **Identifying the Reactions**:
- Glycolysis, the Krebs cycle, and oxidative phosphorylation are the three main stages of cellular respiration. During these processes, glucose (C₆H₁₂O₆) is oxidized, and oxygen is used to produce energy.

3. **Analyzing Glycolysis**:
- In glycolysis, glucose is broken down into pyruvate, and oxygen is not directly used. Therefore, \(^{18}O\) does not appear in any products from this stage.

4. **Analyzing the Krebs Cycle**:
- The Krebs cycle (or citric acid cycle) processes acetyl-CoA derived from pyruvate. In this cycle, carbon dioxide (CO₂) is produced as a waste product. However, the oxygen in CO₂ comes from the original glucose and not from the labeled \(^{18}O\).

5. **Analyzing Oxidative Phosphorylation**:
- In oxidative phosphorylation, oxygen acts as the final electron acceptor in the electron transport chain. Here, \(^{18}O\) from the labeled oxygen will combine with hydrogen ions (H⁺) to form water (H₂O).

6. **Conclusion**:
- The molecule that will become radioactive as a result of using \(^{18}O\) is water (H₂O). When oxygen is incorporated into water, it will carry the radioactive label.

### Final Answer:
The molecules that will become radioactive are **water (H₂O)**.