Assertion`:-` Degree of hydrolysis and pH of a `WAWB` salt is independent of initial concentration of salt.
Reason`:-` The solution of `NH_(4)CN` in water has pH slightly greater than ?

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertiion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states that the degree of hydrolysis and pH of a weak acid weak base (WAWB) salt is independent of the initial concentration of the salt.

- **Degree of Hydrolysis (h)**: For a salt formed from a weak acid and a weak base, the degree of hydrolysis can be expressed as:
\[ h = \sqrt{K_h} \]
where \( K_h = \frac{K_w}{K_a \cdot K_b} \). Here, \( K_w \) is the ion product of water, \( K_a \) is the dissociation constant of the weak acid, and \( K_b \) is the dissociation constant of the weak base.
- **pH Calculation**: The pH of such a salt can be calculated using:
\[ \text{pH} = \frac{1}{2} pK_w + pK_a - pK_b \]

In both expressions, we can see that the initial concentration of the salt does not appear, indicating that the degree of hydrolysis and pH are indeed independent of the initial concentration of the salt.

### Conclusion for Assertion
The assertion is **true**.

### Step 2: Analyze the Reason
The reason states that the solution of \( NH_4CN \) in water has a pH slightly greater than 7.

- When \( NH_4CN \) dissolves in water, it dissociates into \( NH_4^+ \) and \( CN^- \).
- \( NH_4^+ \) is the conjugate acid of the weak base \( NH_3 \) and \( CN^- \) is the conjugate base of the weak acid \( HCN \).
- The pH can be calculated using the formula:
\[ \text{pH} = 7 + \frac{1}{2}(pK_a - pK_b) \]

Since \( HCN \) is a stronger acid than \( NH_4OH \) (the base formed from \( NH_4^+ \)), it follows that \( pK_a < pK_b \). This means the term \( (pK_a - pK_b) \) will be negative, leading to:
\[ \text{pH} < 7 \]
Thus, the statement that the pH is slightly greater than 7 is incorrect.

### Conclusion for Reason
The reason is **false**.

### Final Conclusion
- The assertion is true, but the reason is false. Therefore, the correct option is **C**: Assertion is true, but reason is false.

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