Assertion (A): `pH` of acidic solution is always below `7` at `25^(@)C`.
Reason (R) : At `25^(@)C`, the `pH` of `10^(-8)M HCI` is `8`.

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.

Explanation

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

### Step 1: Understanding the Assertion (A)
The assertion states: "pH of acidic solution is always below 7 at 25°C."

- The pH scale ranges from 0 to 14 at 25°C.
- A pH of 7 is considered neutral (pure water).
- pH values below 7 indicate acidic solutions.
- Therefore, the assertion is correct because any solution that is classified as acidic will have a pH less than 7.

### Step 2: Understanding the Reason (R)
The reason states: "At 25°C, the pH of 10^(-8) M HCl is 8."

- HCl is a strong acid and dissociates completely in solution: HCl → H⁺ + Cl⁻.
- For a 10^(-8) M solution of HCl, the concentration of H⁺ ions contributed by HCl alone is 10^(-8) M.
- However, pure water also contributes H⁺ ions at a concentration of 10^(-7) M (from the autoionization of water).
- Therefore, the total concentration of H⁺ ions in the solution is:
\[ [H^+] = 10^{-8} + 10^{-7} = 1.1 \times 10^{-7} \text{ M} \]
- To find the pH:
\[ \text{pH} = -\log(1.1 \times 10^{-7}) \approx 6.95 \]
- This indicates that the pH is actually less than 7, not 8. Thus, the reason is incorrect.

### Conclusion
- The assertion (A) is correct: pH of acidic solutions is always below 7 at 25°C.
- The reason (R) is incorrect: the pH of 10^(-8) M HCl is not 8, but approximately 6.95.

### Final Answer
- Assertion (A) is true.
- Reason (R) is false.