Which one of the following mixture does not act as a buffer solution?

Options

A. Boric acid and borax
B. Sodium phosphate & disodium hydrogen phosphate
C. Sodium propionate and propionic acid
D. Sod. Acetate and sodium propionate

Answer

To determine which of the following mixtures does not act as a buffer solution, we need to understand the definition of a buffer solution. A buffer solution is typically composed of a weak acid and its conjugate base or a weak base and its conjugate acid. Let's analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Buffer Solutions**:
- A buffer solution consists of a weak acid and its conjugate base or a weak base and its conjugate acid. This allows the solution to resist changes in pH when small amounts of acid or base are added.

2. **Analyzing Option A: Boric Acid and Borax**:
- Boric acid (H3BO3) is a weak acid, and borax (Na2B4O7·10H2O) can act as its conjugate base. Therefore, this combination can act as a buffer solution.

3. **Analyzing Option B: Na3PO4 and Disodium Hydrogen Phosphate**:
- Disodium hydrogen phosphate (Na2HPO4) is a weak base, and sodium phosphate (Na3PO4) can act as its conjugate acid. This combination can also act as a buffer solution.

4. **Analyzing Option C: Sodium Propionate and Propionic Acid**:
- Propionic acid (C2H5COOH) is a weak acid, and sodium propionate (C2H5COONa) is its conjugate base. Thus, this combination can act as a buffer solution.

5. **Analyzing Option D: Sodium Acetate and Sodium Propionate**:
- Sodium acetate (CH3COONa) and sodium propionate (C2H5COONa) are both salts and do not contain a weak acid or weak base. Therefore, this combination does not form a buffer solution.

### Conclusion:
Based on the analysis, the mixture that does not act as a buffer solution is **Option D: Sodium Acetate and Sodium Propionate**.

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