The `P_(50)` value decreses in all of the following conditions,except

Options

A. Fall in` pCO_2`
B. Increase in BPG level
C. Fall in tempareture
D. Fall in `[H^+]` ions

Answer

To solve the question regarding the conditions under which the `P_(50)` value decreases, we need to understand what `P_(50)` represents and how different factors influence it.

### Step-by-Step Solution:

1. **Understanding P50**:
- `P_(50)` is the partial pressure of oxygen at which hemoglobin is 50% saturated with oxygen. A lower `P_(50)` value indicates that hemoglobin binds oxygen more readily, while a higher `P_(50)` value indicates that more oxygen is required for the same level of saturation.

2. **Factors Affecting P50**:
- Several factors can influence the `P_(50)` value:
- **Partial Pressure of CO2 (pCO2)**: An increase in pCO2 leads to a decrease in pH (more acidic conditions), promoting the release of oxygen from hemoglobin (increased `P_(50)`).
- **Partial Pressure of O2 (pO2)**: An increase in pO2 will promote the binding of oxygen to hemoglobin, thus decreasing `P_(50)`.
- **Hydrogen Ion Concentration (H+)**: An increase in H+ (lower pH) will also promote the release of oxygen from hemoglobin, leading to an increased `P_(50)`.
- **Temperature**: Higher temperatures will favor the release of oxygen from hemoglobin, increasing `P_(50)`.

3. **Analyzing the Options**:
- We need to identify which condition does NOT lead to a decrease in `P_(50)`:
- **Option A: Fall in pCO2**: This would lead to an increase in `P_(50)`, as lower pCO2 supports oxygen binding.
- **Option B: Fall in pO2**: A decrease in pO2 would increase `P_(50)`, as less oxygen availability means hemoglobin is less saturated.
- **Option C: Fall in Temperature**: A decrease in temperature would favor oxygen binding, thus decreasing `P_(50)`.
- **Option D: Fall in H+ ions**: A decrease in H+ ions (increased pH) would favor oxygen binding, leading to a decrease in `P_(50)`.

4. **Conclusion**:
- The correct answer is **Option B: Fall in pO2**. This condition does not decrease the `P_(50)` value; instead, it increases it.