Assertion (A): `pH` of buffer chnages with temperature.
Reason (R) : Ionic of a water `(K_(w))` changes with temperature.

Options

A. If both (A) and (R) are correc, and (R) is the correct explanation of (A).
B. If both (A) and (R) are correct but (R) is not the correct explanation of (A).
C. If (A) is correct, but (R) is incorrect.
D. If (A) is incorrect, but (R) is correct.

Answer

To solve the assertion and reasoning question, we will analyze both the assertion (A) and the reason (R) step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the pH of a buffer changes with temperature.
- Buffers are solutions that resist changes in pH upon the addition of small amounts of acids or bases. However, temperature can influence the dissociation of the weak acid and its conjugate base in the buffer solution.

2. **Understanding the Reason (R)**:
- The reason states that the ionic product of water (Kw) changes with temperature.
- Kw is defined as the product of the concentrations of hydrogen ions [H⁺] and hydroxide ions [OH⁻] in water, expressed as Kw = [H⁺][OH⁻].

3. **Analyzing the Relationship**:
- It is known from chemistry that Kw increases with an increase in temperature. This means that at higher temperatures, the concentration of H⁺ ions in water increases, which subsequently affects the pH.
- Since pH is calculated using the formula pH = -log[H⁺], an increase in [H⁺] due to a rise in temperature will lead to a decrease in pH.

4. **Conclusion**:
- Since both the assertion (A) and the reason (R) are true, and the reason correctly explains the assertion, we conclude that:
- Assertion (A) is true: pH of a buffer does change with temperature.
- Reason (R) is true: Kw does change with temperature and affects the pH.

5. **Final Answer**:
- The correct option is that both A and R are correct, and R is the correct explanation for A.