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 regarding the pH of a \(10^{-8}\) M HCl solution and the assertion that HCl is a strong acid, we will go through the following steps:

### Step 1: Understanding the Assertion
The assertion states that the pH of a \(10^{-8}\) M HCl solution is approximately 6.9.

### Step 2: Calculating the Contribution of H⁺ Ions
HCl is a strong acid, which means it dissociates completely in solution. Therefore, the concentration of H⁺ ions contributed by HCl is \(10^{-8}\) M. However, we also need to consider the contribution of H⁺ ions from water, which is \(10^{-7}\) M at neutral conditions.

### Step 3: Total Concentration of H⁺ Ions
The total concentration of H⁺ ions in the solution will be the sum of the H⁺ ions from HCl and the H⁺ ions from water:
\[ \text{Total } [H^+] = [H^+]_{\text{HCl}} + [H^+]_{\text{water}} = 10^{-8} + 10^{-7} \]
To add these, we can factor out \(10^{-7}\):
\[ \text{Total } [H^+] = 10^{-7}(1 + 0.1) = 10^{-7}(1.1) = 1.1 \times 10^{-7} \text{ M} \]

### Step 4: Calculating the pH
The pH is calculated using the formula:
\[ \text{pH} = -\log[H^+] \]
Substituting the total concentration of H⁺ ions:
\[ \text{pH} = -\log(1.1 \times 10^{-7}) = -\log(1.1) - \log(10^{-7}) = 7 - \log(1.1) \]
Using the approximation \(\log(1.1) \approx 0.041\):
\[ \text{pH} \approx 7 - 0.041 \approx 6.959 \]
Thus, the pH is approximately 6.95, which supports the assertion.

### Step 5: Evaluating the Reason
The reason states that HCl is a strong acid. This is true, as HCl completely dissociates in solution. However, while this fact is correct, it does not directly explain why the pH of the \(10^{-8}\) M solution is approximately 6.9.

### Conclusion
Both the assertion and the reason are true, but the reason does not provide a correct explanation for the assertion. Therefore, the correct answer is that both statements are true, but the reason is not a correct explanation of the assertion.

### Final Answer
Both A and R are true, but R is not the correct explanation of A.

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