Which of the following is not an example of buffer solution ?

Options

A. `HNO_(2)+KNO_(2)`
B. HF+KF
C. `PhNH_(2)+PhNH_(3)^(+)Cl^(-)`
D. `NH_(4)Cl+HCl`

Answer

To determine which of the following options is not an example of a buffer solution, we need to understand what constitutes a buffer solution. A buffer solution is defined as a solution that resists changes in pH when small amounts of acid or base are added. Typically, buffer solutions consist of a weak acid and its conjugate base, or a weak base and its conjugate acid.

Let's analyze the options provided:

1. **Option A: HNO2 + KNO2**
- HNO2 (Nitrous acid) is a weak acid, and KNO2 (Potassium nitrite) is the salt of the weak acid. This combination forms a buffer solution because it consists of a weak acid and its conjugate base.

2. **Option B: HF + KF**
- HF (Hydrofluoric acid) is a weak acid, and KF (Potassium fluoride) is the salt of the weak acid. This combination also forms a buffer solution as it consists of a weak acid and its conjugate base.

3. **Option C: PHNH2 + PHNH3Cl**
- PHNH2 (Aniline) is a weak base, and PHNH3Cl (Ammonium chloride) is the salt of the weak base. This combination forms a buffer solution because it consists of a weak base and its conjugate acid.

4. **Option D: NH4Cl + HCl**
- NH4Cl (Ammonium chloride) is a salt derived from a weak base (NH3) and a strong acid (HCl). HCl is a strong acid. This combination does not form a buffer solution because it does not consist of a weak acid and its conjugate base or a weak base and its conjugate acid.

Based on this analysis, the option that is not an example of a buffer solution is:

**Final Answer: Option D (NH4Cl + HCl)**