Which of the following statements is not true ?

Options

A. The partial presure of `O_(2)` in deoxygenated blood in 40mm Hg.
B. The partial preesure of `O_(2)` in oxygenated blood is 95mm Hg
C. The partial pressure of `O_(2)` in alveolar air is 104 mm Hg
D. The partial pressure of` CO_(2)` in alveolar air is 95 mm Hg

Answer

To determine which statement is not true, we need to analyze each of the provided statements regarding the partial pressures of oxygen and carbon dioxide in deoxygenated blood and alveolar air.

### Step-by-Step Solution:

1. **Understanding the Statements**:
- **Statement 1**: The partial pressure of oxygen in deoxygenated blood is 40 mmHg.
- **Statement 2**: The partial pressure of oxygen in deoxygenated blood is 95 mmHg.
- **Statement 3**: The partial pressure of oxygen in alveolar air is 104 mmHg.
- **Statement 4**: The partial pressure of carbon dioxide in alveolar air is 95 mmHg.

2. **Evaluating Statement 1**:
- The partial pressure of oxygen in deoxygenated blood is typically around 40 mmHg. This statement is true.

3. **Evaluating Statement 2**:
- The partial pressure of oxygen in deoxygenated blood cannot be 95 mmHg. This value is more characteristic of oxygenated blood. Therefore, this statement is false.

4. **Evaluating Statement 3**:
- The partial pressure of oxygen in alveolar air is approximately 104 mmHg. This statement is true.

5. **Evaluating Statement 4**:
- The partial pressure of carbon dioxide in alveolar air is generally around 40 mmHg, not 95 mmHg. This statement is also false.

6. **Conclusion**:
- The statements that are not true are Statement 2 and Statement 4. However, since the question asks for one statement that is not true, we can conclude that Statement 2 is the most clearly incorrect regarding the partial pressure of oxygen in deoxygenated blood.

### Final Answer:
The statement that is not true is: **The partial pressure of oxygen in deoxygenated blood is 95 mmHg.**