A : pH of `10^(-8)` M HCI solution is approx 6.9
R : HCI is a strong acid.

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 both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states that the pH of a \(10^{-8}\) M HCl solution is approximately 6.9. To verify this, we need to calculate the pH of the solution.

### Step 2: Calculate the pH of \(10^{-8}\) M HCl
1. **Dissociation of HCl**: HCl is a strong acid and completely dissociates in water:
\[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \]
Therefore, the concentration of \(\text{H}^+\) ions from HCl is \(10^{-8}\) M.

2. **Water Dissociation**: Water also dissociates:
\[ \text{H}_2\text{O} \rightleftharpoons \text{H}^+ + \text{OH}^- \]
The concentration of \(\text{H}^+\) from water at 25°C is \(10^{-7}\) M.

3. **Total \(\text{H}^+\) Concentration**: The total concentration of \(\text{H}^+\) ions in the solution is the sum of the contributions from HCl and water:
\[ [\text{H}^+]_{\text{total}} = 10^{-8} + 10^{-7} = 1.1 \times 10^{-7} \text{ M} \]

### Step 3: Calculate the pH
Using the formula for pH:
\[ \text{pH} = -\log[\text{H}^+] \]
Substituting the total concentration:
\[ \text{pH} = -\log(1.1 \times 10^{-7}) \approx 6.9 \]
Thus, the assertion is correct.

### Step 4: Understand the Reason
The reason states that HCl is a strong acid. This is true because strong acids completely dissociate in solution.

### Step 5: Evaluate the Relationship Between Assertion and Reason
While both the assertion and reason are true, the reason does not explain why the pH of \(10^{-8}\) M HCl is approximately 6.9. The reason for the pH being higher than expected (around 7) is due to the common ion effect, where the presence of HCl affects the dissociation of water.

### Conclusion
- **Assertion**: True (pH is approximately 6.9)
- **Reason**: True (HCl is a strong acid)
- **Explanation**: The reason does not correctly explain the assertion.

### Final Answer
Both assertion and reason are true, but the reason is not the correct explanation for the assertion.