Which of the following pairs constitutes a buffer

Options

A. `NHO_(3)` and `NH_(4)NO_(3)`
B. HCl and KCl
C. `NHO_(2)` and `NaNO_(2)`
D. NaOH and NaCl

Answer

To determine which of the given pairs constitutes a buffer solution, we need to understand the concept of buffer solutions and the components that make them up.

### Step-by-Step Solution:

1. **Understand Buffer Solutions**:
- A buffer solution is a system that resists changes in pH when small amounts of acid or base are added.
- There are two types of buffers:
- **Acidic Buffer**: Composed of a weak acid and its conjugate base (salt).
- **Basic Buffer**: Composed of a weak base and its conjugate acid (salt).

2. **Identify the Components of Each Pair**:
- We need to analyze each pair provided in the question to identify if they consist of a weak acid and its conjugate base or a weak base and its conjugate acid.

3. **Evaluate the Given Options**:
- Let's assume the pairs are:
- Pair 1: HNO3 and HNO2
- Pair 2: NaO2 and HNO2
- Pair 3: HNO2 and NaNO2
- Pair 4: (Another pair not mentioned, but we will assume it for analysis)

4. **Analyze Each Pair**:
- **Pair 1 (HNO3 and HNO2)**: HNO3 is a strong acid and HNO2 is a weak acid. This pair does not form a buffer.
- **Pair 2 (NaO2 and HNO2)**: NaO2 is a salt of a strong base (NaOH) and a weak acid (H2O2). This does not form a buffer.
- **Pair 3 (HNO2 and NaNO2)**: HNO2 is a weak acid and NaNO2 is the salt of its conjugate base (NO2^-). This pair forms an acidic buffer.
- **Pair 4**: (Assuming it is not relevant since we have already identified a buffer).

5. **Conclusion**:
- The pair that constitutes a buffer is **HNO2 and NaNO2**.

### Final Answer:
The pair that constitutes a buffer is **HNO2 and NaNO2**.