A buffer solution can be obtained from

Options

A. HCN and KCN
B. `CH_3COONH_4`
C. `NH_4CI and NH_4OH`
D. All of these

Answer

To determine where a buffer solution can be obtained, we need to understand the components that make up a buffer solution. A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid.

### Step-by-Step Solution:

1. **Understanding Buffer Solutions**:
- A buffer solution maintains a stable pH when small amounts of acids or bases are added.
- It consists of either:
- A weak acid and its conjugate base (acidic buffer).
- A weak base and its conjugate acid (basic buffer).

2. **Identifying Components**:
- **Weak Acid**: An acid that does not completely dissociate in solution (e.g., acetic acid, HCN).
- **Conjugate Base**: The species that remains after the weak acid donates a proton (e.g., acetate ion from acetic acid, CN⁻ from HCN).
- **Weak Base**: A base that does not completely dissociate in solution (e.g., NH₄OH).
- **Conjugate Acid**: The species that forms when the weak base accepts a proton (e.g., NH₄⁺ from NH₄OH).

3. **Analyzing Options**:
- **Option 1**: HCN and KCN
- HCN is a weak acid, and KCN provides the conjugate base (CN⁻). This combination forms a buffer solution.
- **Option 2**: CH₃COONH₄
- This salt can be derived from acetic acid (weak acid) and ammonium hydroxide (weak base). Thus, it can also act as a buffer.
- **Option 3**: NH₄Cl and NH₄OH
- NH₄OH is a weak base, and NH₄Cl provides the conjugate acid (NH₄⁺). This combination forms a mixed buffer.
- **Option 4**: All of the above
- Since all the combinations mentioned can form buffer solutions, this option is correct.

4. **Conclusion**:
- All the provided options can yield buffer solutions. Therefore, the answer is that a buffer solution can be obtained from all of the given combinations.

### Final Answer:
A buffer solution can be obtained from all of the options provided: HCN and KCN, CH₃COONH₄, and NH₄Cl with NH₄OH.

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