Assertion : Oxygen dissociation curve of haemoglobin is sigmoid .
Reason : Oxygen dissociation curve moves towards left side with increse in `CO_(2)` concentration in the air.

Options

A. If both Assertion and Reason are true and Reason is a correct explaintion of Assertion .
B. If both assertion and Reason are true but Reason is not a correct explanation of Assertion .
C. If Assertion is true but Reason is false .
D. If both assertion and Reason are false .

Answer

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

### Step 1: Analyze the Assertion
The assertion states that "Oxygen dissociation curve of haemoglobin is sigmoid."

- **Explanation**: The oxygen dissociation curve of hemoglobin indeed has a sigmoid shape (S-shaped curve). This is due to the cooperative binding of oxygen molecules to hemoglobin. As one oxygen molecule binds to hemoglobin, it increases the affinity of the remaining binding sites for oxygen, leading to a gradual increase in saturation until it levels off.

### Step 2: Analyze the Reason
The reason states that "Oxygen dissociation curve moves towards the left side with an increase in CO₂ concentration in the air."

- **Explanation**: This statement is incorrect. The oxygen dissociation curve actually shifts to the right with an increase in CO₂ concentration. This phenomenon is known as the Bohr effect, where increased levels of CO₂ (and decreased pH) reduce hemoglobin's affinity for oxygen, facilitating oxygen release to tissues that need it.

### Conclusion
- **Assertion**: True (the oxygen dissociation curve is sigmoid).
- **Reason**: False (the curve shifts to the right with increased CO₂ concentration, not left).

### Final Answer
The correct answer is Option 3: "Assertion is True but Reason is False."

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