Which of the following reactions prevails in red blood cells travelling through pulmonary capillaries?

Options

A. `Hb + 4O_2 to Hb(O_2)_4`
B. `Hb(O_2)_4 to Hb + 4O_(ul2)`
C. `H_2CO_3 to H^(+) + HCO_3 `
D. `Hb + (CO_2)_4 to Hb(CO_2)_4`

Explanation

**Step-by-Step Solution:**

1. **Understanding the Context**: The question pertains to the reactions occurring in red blood cells (RBCs) as they travel through the pulmonary capillaries, which are associated with the lungs.

2. **Recognizing the Role of the Lungs**: The lungs facilitate the exchange of gases, specifically the intake of oxygen and the release of carbon dioxide. This process is crucial for maintaining the oxygen supply to body tissues and removing waste gases.

3. **Identifying the Function of Hemoglobin**: Hemoglobin (Hb) is a respiratory pigment found in red blood cells that binds reversibly with oxygen. This binding is essential for transporting oxygen from the lungs to the tissues.

4. **Analyzing the Reaction in the Pulmonary Capillaries**: In the pulmonary capillaries, oxygen from the inhaled air diffuses into the blood, where it binds to hemoglobin. This reaction can be represented as:
\[ \text{Hb} + 4\text{O}_2 \rightarrow \text{Hb(O}_2\text{)}_4 \]
This indicates that one molecule of hemoglobin can bind with four molecules of oxygen, forming oxyhemoglobin.

5. **Excluding Other Options**: The other options presented in the question involve processes that occur in body tissues, not in the pulmonary capillaries:
- Dissociation of oxyhemoglobin occurs in tissues where oxygen is released.
- The formation of bicarbonate ions from carbonic acid occurs in tissues where carbon dioxide is produced.
- Binding of carbon dioxide to hemoglobin (carbaminohemoglobin) also occurs in tissues, not in the lungs.

6. **Conclusion**: The correct reaction that prevails in red blood cells traveling through pulmonary capillaries is the binding of hemoglobin with oxygen to form oxyhemoglobin.

**Final Answer**: The reaction that prevails in red blood cells traveling through pulmonary capillaries is:
\[ \text{Hb} + 4\text{O}_2 \rightarrow \text{Hb(O}_2\text{)}_4 \]

---