When an acid or alkali is mixed with buffer solution, then pH of buffer solution

Options

A. Not changes
B. Can Increase or Decrease
C. Increases
D. Decreases

Explanation

### Step-by-Step Solution:

1. **Understanding Buffer Solutions**:
- A buffer solution is defined as a solution that resists changes in pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid.

2. **Effect of Adding Acid or Base**:
- When a small amount of acid (like HCl) is added to a buffer solution, the weak base present in the buffer will react with the added hydrogen ions (H⁺) from the acid. This reaction helps to minimize the change in pH.
- Conversely, when a small amount of base (like NaOH) is added, the weak acid in the buffer will react with the hydroxide ions (OH⁻) from the base, again helping to maintain the pH.

3. **Conclusion on pH Change**:
- Because of the buffer action, the pH of the buffer solution remains relatively constant despite the addition of small amounts of acid or base. Therefore, we can conclude that the pH of the buffer solution does not change significantly when small amounts of acid or alkali are mixed with it.

### Final Answer:
When an acid or alkali is mixed with a buffer solution, the pH of the buffer solution remains relatively unchanged.

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