A buffer solution can be prepared from a mixture of
1. Sodium acetate and acetic acid in water
2. Excess sodium acetate and hydrochloric acid in water
3. Ammonia and ammonia chloride in water
4. Ammonia and sodium hydroxide in water.

Options

A. `1,3,4`
B. `2,3,4`
C. `1,2,4`
D. `1,2,3`

Answer

To determine which mixtures can form a buffer solution, we first need to understand what a buffer solution is. A buffer solution is one that resists changes in pH when small amounts of acid or base are added. There are two types of buffer solutions: acidic buffers and basic buffers.

### Step-by-Step Solution:

1. **Identify the Components of Each Option:**
- **Option 1:** Sodium acetate (CH₃COONa) and acetic acid (CH₃COOH) in water.
- **Option 2:** Excess sodium acetate (CH₃COONa) and hydrochloric acid (HCl) in water.
- **Option 3:** Ammonia (NH₃) and ammonium chloride (NH₄Cl) in water.
- **Option 4:** Ammonia (NH₃) and sodium hydroxide (NaOH) in water.

2. **Analyze Option 1:**
- Sodium acetate is the salt of a weak acid (acetic acid), and when mixed with acetic acid, it forms an acidic buffer.
- **Conclusion:** This option can form a buffer solution.

3. **Analyze Option 2:**
- Here, we have excess sodium acetate (a salt of a weak acid) and hydrochloric acid (a strong acid).
- The presence of excess sodium acetate means that after the reaction with HCl, we will still have the weak acid (acetic acid) and its salt (sodium acetate) in solution.
- **Conclusion:** This option can also form a buffer solution.

4. **Analyze Option 3:**
- Ammonia (NH₃) is a weak base, and ammonium chloride (NH₄Cl) is the salt of that weak base.
- This combination will create a basic buffer solution.
- **Conclusion:** This option can form a buffer solution.

5. **Analyze Option 4:**
- In this case, we have ammonia (a weak base) and sodium hydroxide (a strong base).
- Mixing a weak base with a strong base does not create a buffer solution, as there is no weak acid or salt present to resist pH changes.
- **Conclusion:** This option cannot form a buffer solution.

### Final Conclusion:
The mixtures that can form buffer solutions are:
- Option 1: Sodium acetate and acetic acid in water.
- Option 2: Excess sodium acetate and hydrochloric acid in water.
- Option 3: Ammonia and ammonium chloride in water.

Thus, the correct options are 1, 2, and 3.