A : At higher temperature , `K_w` of water remains unaltered.
R: `k_w` is a constant.

Options

A. If both Assertion & Reason are true and the reason in the corret explanation of the assertion, then mark
B. If both assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark
C. If Assertion is true statement but Reason is false then mark
D. If both Assertion and Reason are false statements , then mark

Answer

To solve the question, we need to analyze the assertion and the reason provided:

**Assertion (A):** At higher temperature, \( K_w \) of water remains unaltered.
**Reason (R):** \( K_w \) is a constant.

### Step-by-Step Solution:

1. **Understanding \( K_w \):**
- \( K_w \) is the ion product of water, defined as \( K_w = [H^+][OH^-] \).
- It represents the equilibrium constant for the self-ionization of water.

2. **Effect of Temperature on \( K_w \):**
- The self-ionization of water is an endothermic process, meaning it absorbs heat.
- According to Le Chatelier's principle, if the temperature of an endothermic reaction is increased, the equilibrium shifts to favor the formation of products (in this case, \( H^+ \) and \( OH^- \) ions).

3. **Conclusion on Assertion:**
- As the temperature increases, the concentrations of \( H^+ \) and \( OH^- \) ions increase, leading to an increase in \( K_w \).
- Therefore, the assertion that \( K_w \) remains unaltered at higher temperatures is **false**.

4. **Conclusion on Reason:**
- The reason states that \( K_w \) is a constant. However, since \( K_w \) changes with temperature, this statement is also **false**.

5. **Final Evaluation:**
- Both the assertion and the reason are incorrect.

### Final Answer:
Both the assertion and the reason are false.