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, we need to analyze the assertion and the reason provided.

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

- **Explanation**: NaCl is a neutral salt formed from a strong acid (HCl) and a strong base (NaOH). In a solution, NaCl dissociates into Na⁺ and Cl⁻ ions. These ions do not hydrolyze (react with water) to produce H⁺ or OH⁻ ions. Therefore, the concentration of H⁺ and OH⁻ ions remains unchanged, and the pH of the solution remains neutral at 7.

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

- **Explanation**: When a solution is diluted, the concentration of all ions decreases. However, in the case of NaCl, since it does not affect the concentration of H⁺ and OH⁻ ions, the pH remains unchanged even upon dilution. Therefore, the statement that the pH decreases upon dilution is false.

### Conclusion
- The assertion is true: pH of 1 M NaCl solution is indeed 7 at 25°C.
- The reason is false: pH does not decrease when the solution is diluted.

### Final Answer
The correct option is: **3. If the assertion is a true statement, but the reason is false.**

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