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 which combinations can form a buffer solution, we need to understand the definition of a buffer solution. A buffer solution is one that can resist changes in pH when small amounts of acid or base are added. Buffers typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid.

### Step-by-Step Solution:

1. **Identify the Components**: We have the following options:
- Option 1: HCN and KCN
- Option 2: CH3COONH4
- Option 3: NH4Cl and NH4OH
- Option 4: All of the above

2. **Examine Option 1: HCN and KCN**:
- HCN (hydrogen cyanide) is a weak acid.
- KCN (potassium cyanide) is the salt of the conjugate base (CN⁻) of HCN.
- Since we have a weak acid and its conjugate base, this combination can form a buffer solution.

3. **Examine Option 2: CH3COONH4**:
- CH3COONH4 (ammonium acetate) is formed from acetic acid (a weak acid) and NH4OH (ammonium hydroxide, a weak base).
- This salt is a combination of a weak acid and a weak base, thus it can also act as a buffer solution.

4. **Examine Option 3: NH4Cl and NH4OH**:
- NH4Cl (ammonium chloride) provides NH4⁺ ions, which is the conjugate acid of the weak base NH4OH (ammonium hydroxide).
- This combination of a weak base and its conjugate acid also forms a buffer solution.

5. **Conclusion**: Since all three options can form buffer solutions, the correct answer is:
- **Option 4: All of these**