Which of the following is a buffer solution?

Options

A. A solution of `KC1` and `KOH`
B. A solution of `CH_(3)COONH_(4)`
C. A solution of `K_(2)SO_(4)` and `NH_(4)OH`
D. A solution of `PhCOOK` nad `PhCOOH`

Explanation

To determine which of the given options is a buffer solution, we need to understand the definition and composition of buffer solutions. A buffer solution is a solution that can resist changes in pH when small amounts of an acid or a base are added. There are two main types of buffer solutions:

1. **Acidic Buffer**: This consists of a weak acid and its salt (which is derived from a strong base).
2. **Basic Buffer**: This consists of a weak base and its salt (which is derived from a strong acid).

Now, let's analyze each option step by step:

### Step 1: Analyze Option 1 - KCl + KOH
- **KCl**: This is a salt formed from a strong acid (HCl) and a strong base (KOH).
- **KOH**: This is a strong base.
- **Conclusion**: Since both components are derived from strong acids and bases, this combination does not form a buffer solution.

### Step 2: Analyze Option 2 - CH3COONH4
- **CH3COONH4**: This is ammonium acetate, which is a salt formed from a weak acid (acetic acid) and a weak base (ammonia).
- **Conclusion**: While it is a salt, it does not consist of a weak acid and its conjugate base or a weak base and its conjugate acid in a way that would create a buffer system. Thus, it does not qualify as a buffer solution.

### Step 3: Analyze Option 3 - K2SO4 + NH4OH
- **K2SO4**: This is a salt derived from a strong acid (H2SO4) and a strong base (KOH).
- **NH4OH**: This is a weak base (ammonium hydroxide).
- **Conclusion**: Since K2SO4 is derived from strong acid and base, this combination does not form a buffer solution.

### Step 4: Analyze Option 4 - CH3COOK + CH3COOH
- **CH3COOK**: This is a salt of a weak acid (acetic acid) and a strong base (potassium hydroxide).
- **CH3COOH**: This is acetic acid, a weak acid.
- **Conclusion**: This combination consists of a weak acid (CH3COOH) and its salt (CH3COOK), which makes it a buffer solution.

### Final Answer
The correct option that represents a buffer solution is **Option 4: CH3COOK + CH3COOH**.

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