Which of the following pair of solutions can act as buffer solution?

Options

A. 0.1 molar aq.NaCl
B. 0.1 molar aq.CH3COOH+0.1 molar NaOH
C. 0.1 molar aq.ammonium acetate
D. 0.1 molar H3PO4

Answer

To determine which pair of solutions can act as a buffer solution, we first need to understand what a buffer solution is. A buffer solution is an aqueous solution that consists of a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid.

Now, let's analyze the given pairs of solutions step by step:

### Step 1: Identify the Components of Each Pair
1. **Pair 1:** 0.1 M HCl (strong acid) and 0.1 M NaCl (neutral salt)
2. **Pair 2:** 0.1 M CH₃COOH (acetic acid, weak acid) and 0.1 M NaOH (strong base)
3. **Pair 3:** 0.1 M ammonium acetate (NH₄C₂H₃O₂, weak acid and conjugate base)
4. **Pair 4:** 0.1 M H₃PO₄ (phosphoric acid, strong acid)

### Step 2: Analyze Each Pair
- **Pair 1 (HCl and NaCl):**
- HCl is a strong acid and does not have a conjugate base present in the solution. Therefore, this pair **cannot** act as a buffer.

- **Pair 2 (CH₃COOH and NaOH):**
- When NaOH (strong base) is added to CH₃COOH (weak acid), it will neutralize some of the acetic acid to form acetate ions (CH₃COO⁻). This results in a mixture of a weak acid and its conjugate base, thus this pair **can** act as a buffer.

- **Pair 3 (Ammonium Acetate):**
- Ammonium acetate is a salt formed from a weak acid (acetic acid) and a weak base (ammonium hydroxide). This solution can resist changes in pH upon the addition of small amounts of acids or bases, so it **can** act as a buffer.

- **Pair 4 (H₃PO₄):**
- H₃PO₄ is a strong acid and does not have a conjugate base present in the solution. Therefore, this pair **cannot** act as a buffer.

### Step 3: Conclusion
Based on the analysis, the pairs that can act as buffer solutions are:
- **Pair 2:** 0.1 M CH₃COOH and 0.1 M NaOH
- **Pair 3:** 0.1 M ammonium acetate

Thus, the correct answer is that the pairs that can act as buffer solutions are **Pair 2 and Pair 3**.

### Final Answer
The pairs of solutions that can act as buffer solutions are:
- 0.1 M CH₃COOH and 0.1 M NaOH
- 0.1 M ammonium acetate