Out of the following , which pair of solutions is not a buffer solution ?

Options

A. `NH_(4)Cl + NH_(4)OH`
B. `NaCl + NH_(4)OH`
C. `Na_(2)HPO_(4) + Na_(3)PO_(4)`
D. `CH_(3)COOH + CH_(3)COONa`

Answer

To determine which pair of solutions is not a buffer solution, we need to understand the definition of buffer solutions and analyze each pair given in the question.

### Step-by-step Solution:

1. **Understand Buffer Solutions**:
- A buffer solution is one that resists changes in pH upon the addition of small amounts of an acid or a base.
- There are two types of buffer solutions:
- **Acidic Buffer**: Formed from a weak acid and its conjugate base (salt).
- **Basic Buffer**: Formed from a weak base and its conjugate acid (salt).

2. **Analyze the Given Pairs**:
- **Pair 1: NH4Cl and NH4OH**
- NH4OH (ammonium hydroxide) is a weak base.
- NH4Cl is a salt formed from a weak base (NH4OH) and a strong acid (HCl).
- This combination forms a basic buffer solution.

- **Pair 2: NH4OH and NaCl**
- NH4OH is a weak base.
- NaCl is a salt formed from a strong acid (HCl) and a strong base (NaOH).
- This combination does not provide a weak acid or a weak base with its conjugate counterpart, hence it does not form a buffer solution.

- **Pair 3: Na2HPO4 and Na3PO4**
- Na2HPO4 is the salt of a weak acid (H2PO4-) and a strong base (NaOH).
- Na3PO4 is a salt of a weak base (PO4^3-) and a strong acid.
- This combination forms a basic buffer solution.

- **Pair 4: Acetic Acid and Sodium Acetate**
- Acetic acid is a weak acid.
- Sodium acetate is the salt of acetic acid and a strong base (NaOH).
- This combination forms an acidic buffer solution.

3. **Conclusion**:
- From the analysis, the pair that does not form a buffer solution is **Pair 2: NH4OH and NaCl**.

### Final Answer:
The pair of solutions that is not a buffer solution is **NH4OH and NaCl**.