A : pH of 1 M NaCI solution is 7 at `25^@C`.
R : pH of this solution decreases when it is diluted 100 times

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 regarding the assertion and reasoning about the pH of a 1 M NaCl solution, let's break it down step by step.

### Step 1: Analyze the Assertion
**Assertion:** The pH of 1 M NaCl solution is 7 at 25°C.

- **Explanation:** NaCl (sodium chloride) is formed from the neutralization reaction between a strong acid (HCl) and a strong base (NaOH). The resulting salt, NaCl, is a neutral salt because it does not hydrolyze in water. Therefore, the pH of a 1 M NaCl solution is indeed 7, which is the same as the pH of pure water at 25°C.

### Step 2: Analyze the Reason
**Reason:** The pH of this solution decreases when it is diluted 100 times.

- **Explanation:** When NaCl is diluted, the concentration of NaCl decreases, but since NaCl is a neutral salt, it does not affect the pH of the solution. The pH remains at 7 even when diluted because the solution still consists primarily of water, which has a pH of 7. Therefore, the reasoning provided is incorrect.

### Conclusion
- The assertion is **True**: The pH of a 1 M NaCl solution is 7.
- The reason is **False**: The pH does not decrease upon dilution; it remains 7.

### Final Answer
- Assertion is true, and Reason is false.

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