Which of the following solutions can act as buffer ?

Options

A. `0.1 ` molar aq. NaCl
B. `0.1` molar aq. `CH_(3)COOH + 0.1 ` M aq NaOH
C. `0.1` molar aq. Ammonium acetate
D. None of the above

Answer

To determine which of the given solutions can act as a buffer, we first need to understand the criteria for a solution to function as a buffer. A buffer solution is one that can resist changes in pH upon the addition of small amounts of acid or base. There are two main types of buffers:

1. **Acidic Buffer**: Composed of a weak acid and its salt (which is formed from a strong base).
2. **Basic Buffer**: Composed of a weak base and its salt (which is formed from a strong acid).

Now, let's analyze the provided options step-by-step:

### Step 1: Analyze Option 1 - 0.1 M Aqueous NaCl
- **Components**: NaCl is formed from NaOH (a strong base) and HCl (a strong acid).
- **Buffer Status**: This solution contains only a salt and does not include a weak acid or a weak base. Therefore, it cannot act as a buffer.

### Step 2: Analyze Option 2 - 0.1 M Aqueous Acetic Acid and 0.1 M NaOH
- **Components**: Acetic acid (CH₃COOH) is a weak acid, and NaOH is a strong base.
- **Reaction**: When mixed, they will react to form sodium acetate (CH₃COONa) and water.
- **Buffer Status**: Although acetic acid is a weak acid, the presence of NaOH (a strong base) means we do not have both a weak acid and its salt present together in the solution. Thus, this combination cannot act as a buffer.

### Step 3: Analyze Option 3 - 0.1 M Aqueous Ammonium Acetate
- **Components**: Ammonium acetate is the salt formed from acetic acid (weak acid) and ammonium hydroxide (weak base).
- **Buffer Status**: This solution contains both a weak acid (from acetic acid) and a weak base (from ammonium hydroxide). However, since it only consists of the salt and does not have a separate weak acid or weak base present, it does not meet the criteria for a buffer solution.

### Step 4: Analyze Option 4 - None of the Above
- Since none of the previous options qualify as buffer solutions based on the criteria discussed, this option is correct.

### Conclusion:
The correct answer is **Option 4: None of the Above**. None of the provided solutions can act as a buffer.