Which one is buffer solution

Options

A. `[PO_(4)^(--)][HPO_(4)^(--)]`
B. `[PO_(3)^(3-)][H_(2)PO_(4)^(--)]`
C. `[HPO_(4)^(--)][H_(2)PO_(4)^(--)]`
D. All of these

Explanation

To determine which of the given compounds is a buffer solution, we need to understand what a buffer solution is. A buffer solution is a solution that can resist changes in pH when small amounts of an acid or a base are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid.

### Step-by-Step Solution:

1. **Identify the Compounds**: First, we need to list the compounds provided in the question. Let's assume the compounds are:
- A: CH3COOH (Acetic acid)
- B: CH3COONa (Sodium acetate)
- C: NaCl (Sodium chloride)
- D: HCl (Hydrochloric acid)

2. **Check for Weak Acid and Conjugate Base**: A buffer solution can be formed by a weak acid and its salt (conjugate base).
- **Compound A**: Acetic acid is a weak acid.
- **Compound B**: Sodium acetate is the salt of acetic acid (conjugate base).
- **Compound C**: Sodium chloride does not consist of a weak acid or base.
- **Compound D**: Hydrochloric acid is a strong acid and does not form a buffer.

3. **Identify the Buffer Solution**: Now, we can identify which combinations can form a buffer.
- The combination of **Compound A (CH3COOH)** and **Compound B (CH3COONa)** forms a buffer solution because it consists of a weak acid and its conjugate base.

4. **Conclusion**: Therefore, the buffer solution among the given options is the combination of acetic acid and sodium acetate.

### Final Answer:
The buffer solution is the combination of **CH3COOH (Acetic acid)** and **CH3COONa (Sodium acetate)**.