Choose the correct statement regarding the partial pressures of respiratory gases.

Options

A. `pCO_2` is more than that of `O_2` in atmosphere.
B. `pCO_2` in oxygenated blood is equal to partial pressure of` O_2` in deoxygenated blood
C. Solubility of `CO_2` is 20-25 time lesser than `O_2`
D. `pCO_2` in tissues is equal to `O_2` partial pressure in oxygenated blood.

Answer

To solve the question regarding the correct statement about the partial pressures of respiratory gases, we will analyze each statement provided and determine its accuracy step by step.

### Step-by-Step Solution:

1. **Understanding Partial Pressures**:
- Partial pressure refers to the pressure exerted by a single type of gas in a mixture of gases. In the context of respiration, we are primarily concerned with oxygen (O2) and carbon dioxide (CO2).

2. **Evaluating the First Statement**:
- The first statement claims that the partial pressure of carbon dioxide (CO2) is more than that of oxygen (O2) in the atmosphere.
- **Analysis**: This statement is incorrect. In the atmosphere, the partial pressure of O2 is significantly higher than that of CO2. Therefore, this statement is false.

3. **Evaluating the Second Statement**:
- The second statement states that the partial pressure of CO2 in oxygenated blood is equal to the partial pressure of O2 in deoxygenated blood.
- **Analysis**: This statement is correct. In oxygenated blood, the concentration of O2 is high, and CO2 is low, while in deoxygenated blood, the situation is reversed. The partial pressures of CO2 in oxygenated blood and O2 in deoxygenated blood are equal due to gas exchange processes in the lungs and tissues.

4. **Evaluating the Third Statement**:
- The third statement claims that the solubility of CO2 is 20 to 25 times lesser than that of O2.
- **Analysis**: This statement is incorrect. The solubility of CO2 in blood is actually 20 to 25 times greater than that of O2, making this statement false.

5. **Evaluating the Fourth Statement**:
- The fourth statement suggests that the partial pressure of CO2 in tissue is equal to the partial pressure of O2 in oxygenated blood.
- **Analysis**: This statement is also incorrect. There is no direct relationship that equates the partial pressure of CO2 in tissues with that of O2 in oxygenated blood, making this statement false.

### Conclusion:
After evaluating all the statements, the only correct statement is the second one: **The partial pressure of CO2 in oxygenated blood is equal to the partial pressure of O2 in deoxygenated blood**.

### Final Answer:
The correct statement regarding the partial pressures of respiratory gases is the second statement.

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