Haldane believes oxyhaemoglobin to act as

Options

A. Acid
B. Alkali
C. Buffer
D. None of the above

Explanation

To solve the question regarding Haldane's belief about oxyhemoglobin, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Oxyhemoglobin**:
- Oxyhemoglobin is formed when oxygen binds to hemoglobin in red blood cells. This process is crucial for transporting oxygen from the lungs to tissues throughout the body.

2. **Haldane's Hypothesis**:
- The scientist J.B.S. Haldane proposed that the formation of oxyhemoglobin is associated with the release of hydrogen ions (H+). This means that when hemoglobin binds to oxygen, it can also lead to the release of protons.

3. **Acidic Nature**:
- The release of H+ ions indicates that oxyhemoglobin has acidic properties. In chemistry, a substance that donates protons (H+) is classified as an acid. Therefore, the presence of H+ ions suggests that oxyhemoglobin can act as an acid.

4. **Dissociation Curve**:
- The oxygen-hemoglobin dissociation curve illustrates how readily hemoglobin acquires and releases oxygen. Haldane's theory further supports that the behavior of oxyhemoglobin in this curve reflects its acidic nature.

5. **Conclusion**:
- Based on Haldane's observations, we conclude that oxyhemoglobin acts as an acid. Therefore, the correct answer to the question is option A: acid.

### Final Answer:
- **Oxyhemoglobin acts as an acid according to Haldane.**