Decrease in `P_(co_(2))` moves the oxygen dissociative curve towards right side/left side.

Answer

To determine the effect of a decrease in \( P_{CO_2} \) on the oxygen dissociation curve, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Oxygen Dissociation Curve**: The oxygen dissociation curve illustrates the relationship between the partial pressure of oxygen (\( P_{O_2} \)) and the percentage saturation of hemoglobin with oxygen. The x-axis represents \( P_{O_2} \), while the y-axis represents hemoglobin saturation.

2. **Identify Factors Affecting the Curve**: Several factors influence the position of the oxygen dissociation curve, including temperature, pH (H+ concentration), and \( P_{CO_2} \). An increase in \( P_{CO_2} \), temperature, or H+ concentration typically shifts the curve to the right, indicating a lower affinity of hemoglobin for oxygen (more oxygen is released).

3. **Effect of Decreasing \( P_{CO_2} \)**: When \( P_{CO_2} \) decreases, it indicates a lower concentration of carbon dioxide in the blood. This condition favors the formation of oxyhemoglobin, meaning hemoglobin has a higher affinity for oxygen.

4. **Direction of Shift**: Since a decrease in \( P_{CO_2} \) promotes the binding of oxygen to hemoglobin, the oxygen dissociation curve will shift to the left. This shift means that at the same partial pressure of oxygen, hemoglobin will be more saturated with oxygen compared to a higher \( P_{CO_2} \) condition.

5. **Conclusion**: Therefore, a decrease in \( P_{CO_2} \) moves the oxygen dissociation curve towards the left side.

### Final Answer:
A decrease in \( P_{CO_2} \) moves the oxygen dissociation curve towards the **left side**.

---