Which of the following solutions will resist change in their pH on moderate dilution?

Options

A. A solution which is 0.1 M in `PhNH_(2)` and 0.2 M in `PhNH_(3)^(+)Cl^(-)`
B. 0.1 M `NaHCO_(3)`
C. A solution obtained by mixing equal volumes of 0.1 M NaOH and 0.2 M PhOH.
D. 0.4 M `CH_(3)COONH_(4)`

Explanation

To determine which solutions will resist changes in their pH upon moderate dilution, we need to evaluate the properties of each solution provided in the question. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Understanding Buffer Solutions
Buffer solutions are mixtures that can maintain a relatively constant pH when small amounts of acid or base are added. They typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid.

**Hint:** Look for solutions that contain a weak acid and its conjugate base or a weak base and its conjugate acid.

### Step 2: Identifying Amphiprotic Species
Amphiprotic species can act as either an acid or a base. They can accept or donate protons, which allows them to help stabilize pH levels in a solution.

**Hint:** Check if the solution contains a species that can both donate and accept protons.

### Step 3: Analyzing Salt Solutions
Salts formed from weak acids and weak bases can also act as buffers. They can resist changes in pH because they can react with added acids or bases.

**Hint:** Look for salts derived from weak acids and weak bases in the solution.

### Step 4: Evaluating Each Given Solution
1. **Solution 1: 0.1 M NH2 and 0.2 M NH3 + Cl⁻**
- This is a buffer solution (weak base NH3 and its conjugate acid NH4⁺). It will resist pH changes.

2. **Solution 2: 0.1 M NaHCO3**
- Sodium bicarbonate (NaHCO3) is an amphiprotic species. It can act as both an acid and a base, thus it will resist pH changes.

3. **Solution 3: Mixing equal volumes of 0.5 M NaOH and 0.5 M HCl**
- This creates a buffer solution (water and salt). It will resist pH changes.

4. **Solution 4: 0.4 M CH3COONH4**
- This is a salt of a weak acid (acetic acid, CH3COOH) and a weak base (ammonium hydroxide, NH4OH). It will also resist pH changes.

### Conclusion
All the solutions listed (A, B, C, and D) will resist changes in their pH upon moderate dilution.

**Final Answer:** A, B, C, and D.