A : pH of 0.1 M HCI solution is less than 0.1 M HCN solution
R : In equimolar solutions , the number of ionisable `H^+` present in HCI is less than present in HCN solution .

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-by-Step Solution:

1. **Understanding the Assertion:**
- The assertion states that the pH of a 0.1 M HCl solution is less than that of a 0.1 M HCN solution.
- HCl is a strong acid and dissociates completely in solution:
\[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \]
- Therefore, in a 0.1 M HCl solution, the concentration of \(\text{H}^+\) ions is 0.1 M.

2. **Understanding the pH Calculation for HCl:**
- The pH is calculated using the formula:
\[ \text{pH} = -\log[\text{H}^+] \]
- For the 0.1 M HCl solution:
\[ \text{pH} = -\log(0.1) = 1 \]

3. **Understanding the Reason:**
- The reason states that in equimolar solutions, the number of ionizable \(\text{H}^+\) present in HCl is less than that in HCN.
- HCN is a weak acid and does not dissociate completely:
\[ \text{HCN} \rightleftharpoons \text{H}^+ + \text{CN}^- \]
- In a 0.1 M HCN solution, the dissociation is partial, meaning the concentration of \(\text{H}^+\) ions will be less than 0.1 M.

4. **Comparing the Ionizable \(\text{H}^+\) Concentrations:**
- Since HCl completely dissociates, the concentration of \(\text{H}^+\) ions from HCl is 0.1 M.
- For HCN, due to partial dissociation, the concentration of \(\text{H}^+\) ions will be less than 0.1 M.
- Thus, the assertion is true, while the reason is false.

5. **Conclusion:**
- The assertion is true: pH of 0.1 M HCl < pH of 0.1 M HCN.
- The reason is false: the number of ionizable \(\text{H}^+\) in HCl is greater than in HCN.

### Final Answer:
- The correct option is that the assertion is true, and the reason is false.

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