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 given assertion and reason question, we will analyze the statements step by step.

### Step 1: Understand 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, which means it completely dissociates in water:
\[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \]
Therefore, in a 0.1 M HCl solution, the concentration of \(\text{H}^+\) ions is 0.1 M.

- **HCN** is a weak acid, which means it does not completely dissociate in water. The dissociation can be represented as:
\[ \text{HCN} \rightleftharpoons \text{H}^+ + \text{CN}^- \]
In a 0.1 M HCN solution, the concentration of \(\text{H}^+\) ions will be less than 0.1 M because only a fraction of HCN molecules dissociate.

### Step 2: Compare the pH Values
The pH of a solution is calculated using the formula:
\[ \text{pH} = -\log[\text{H}^+] \]
Since the concentration of \(\text{H}^+\) ions in the HCl solution (0.1 M) is greater than that in the HCN solution, the pH of the HCl solution will be lower than that of the HCN solution.

### Conclusion for Assertion
- The assertion is **true**: pH of 0.1 M HCl < pH of 0.1 M HCN.

### Step 3: Understand the Reason
The reason states that in equimolar solutions, the number of ionizable \(\text{H}^+\) present in HCl is less than that present in HCN.

- As established earlier, HCl completely dissociates, providing 0.1 M \(\text{H}^+\) ions.
- HCN, being a weak acid, provides significantly fewer \(\text{H}^+\) ions than 0.1 M.

### Conclusion for Reason
- The reason is **false**: the number of ionizable \(\text{H}^+\) in HCl is greater than in HCN.

### Final Evaluation
- The assertion is true, and the reason is false. Therefore, the correct option is that the assertion is true, but the reason is false.

### Answer
The correct answer is **Option 3**: Assertion is true, Reason is false.

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