Assertion: `0.1 M NaCN+0.05 M HCl` solution on mixing in equal volume forms a buffer solution.
Reason : The solution after mixing contains a weak acid and its conjugate base and thus acts as buffer.

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 problem, we need to analyze the assertion and reason given in the question step by step.

### Step 1: Understanding the Components
The assertion states that mixing `0.1 M NaCN` and `0.05 M HCl` in equal volumes forms a buffer solution.

- **NaCN** is the sodium salt of the weak acid **HCN** (hydrocyanic acid).
- **HCl** is a strong acid.

### Step 2: Mixing the Solutions
When we mix equal volumes of `0.1 M NaCN` and `0.05 M HCl`, we need to determine the concentrations of the components after mixing.

- The total volume after mixing is doubled, so the concentrations will change.
- The concentration of NaCN after mixing will be:
\[ \text{Concentration of NaCN} = \frac{0.1 \, \text{M} \times 1 \, \text{L}}{2 \, \text{L}} = 0.05 \, \text{M} \]
- The concentration of HCl after mixing will be:
\[ \text{Concentration of HCl} = \frac{0.05 \, \text{M} \times 1 \, \text{L}}{2 \, \text{L}} = 0.025 \, \text{M} \]

### Step 3: Reaction Between NaCN and HCl
Next, we consider the reaction that occurs when NaCN and HCl are mixed:
\[ \text{NaCN} + \text{HCl} \rightarrow \text{HCN} + \text{NaCl} \]
- Here, HCl will react with NaCN to produce HCN (weak acid) and NaCl (salt).

### Step 4: Limiting Reagent
In this reaction:
- We have `0.05 M NaCN` and `0.025 M HCl`.
- HCl is the limiting reagent because it will be completely consumed first.

### Step 5: Final Concentrations
After the reaction:
- `0.025 M HCl` will react with `0.025 M NaCN`, leaving:
- `0.025 M NaCN` unreacted.
- `0.025 M HCN` produced.

### Step 6: Buffer Solution Formation
The resulting solution contains:
- A weak acid (HCN) and its conjugate base (CN⁻ from NaCN).
- This combination of a weak acid and its conjugate base indeed forms a buffer solution.

### Conclusion
Both the assertion and reason are true:
- **Assertion**: The mixture forms a buffer solution.
- **Reason**: The solution contains a weak acid and its conjugate base.

Thus, the correct answer is:
**Option A**: Both assertion and reason are true, and the reason is the correct explanation for the assertion.

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