Assertion : A rise in `PCO_(2), H^(+)` ions and temperature shifts the `HbO_(2)` dissociation curve to right.
Reason : A rise in `PCO_(2)` or fall in pH decreases oxygen affinity for haemoglobin.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true and reason is not the correct explanation of assertion
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

To solve the assertion and reason question regarding the oxyhemoglobin dissociation curve, we will analyze both statements step by step.

### Step 1: Understanding the Assertion
The assertion states: "A rise in `PCO_(2)`, `H^(+)` ions, and temperature shifts the `HbO_(2)` dissociation curve to the right."

- The oxyhemoglobin dissociation curve is a graph that shows the relationship between the partial pressure of oxygen (`PO2`) and the saturation of hemoglobin with oxygen.
- A rightward shift in this curve indicates a decrease in hemoglobin's affinity for oxygen, meaning hemoglobin releases oxygen more readily.

### Step 2: Factors Affecting the Oxyhemoglobin Dissociation Curve
The assertion mentions three factors:
1. **Partial Pressure of CO2 (`PCO2`)**: An increase in `PCO2` leads to a decrease in pH (more acidic conditions), which decreases hemoglobin's affinity for oxygen.
2. **Hydrogen Ions (`H+`)**: An increase in `H+` concentration (lower pH) also decreases hemoglobin's affinity for oxygen.
3. **Temperature**: An increase in temperature decreases the affinity of hemoglobin for oxygen.

### Step 3: Conclusion on the Assertion
Since all three factors mentioned (increased `PCO2`, increased `H+`, and increased temperature) lead to a rightward shift of the oxyhemoglobin dissociation curve, the assertion is **true**.

### Step 4: Understanding the Reason
The reason states: "A rise in `PCO_(2)` or fall in pH decreases oxygen affinity for hemoglobin."

- This statement is also true. An increase in `PCO2` results in more carbonic acid formation, which increases `H+` concentration and lowers pH, both of which decrease hemoglobin's affinity for oxygen.

### Step 5: Conclusion on the Reason
The reason correctly explains the assertion. Therefore, the reason is also **true**.

### Final Conclusion
Both the assertion and the reason are true, and the reason correctly explains the assertion. Thus, the correct answer is that both statements are true, and the reason is the correct explanation of the assertion.

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