Which one of the following is not a buffer solution ?

Options

A. `0.8M H_2S + 0.8 M kHS`
B. `2M C_6H_5NH_2 + 2M C_6H_5NH_3^+ Br^-`
C. `3M H_2CO_3 + 3M KHCO_3`
D. `0.05 M KClO_4 + 0.05M HClO_4`

Explanation

To determine which of the following options is not a buffer solution, we first need to understand what a buffer solution is. A buffer solution is a system that resists changes in pH upon the addition of small amounts of acid or base. There are two types of buffer solutions:

1. **Acidic Buffer**: This consists of a weak acid and its conjugate base (or salt).
2. **Basic Buffer**: This consists of a weak base and its conjugate acid (or salt).

Now, let's analyze the options provided:

1. **H2S and KHS**:
- H2S (hydrogen sulfide) is a weak acid.
- KHS (potassium hydrogen sulfide) is the salt of H2S with a strong base (KOH).
- This combination forms an acidic buffer solution.

2. **Aniline and its salt**:
- Aniline is a weak base.
- The salt formed with a strong acid (like HCl) would be anilinium chloride.
- This combination forms a basic buffer solution.

3. **H2CO3 and its salt**:
- H2CO3 (carbonic acid) is a weak acid.
- The salt (like NaHCO3) is formed with a strong base (like NaOH).
- This combination forms an acidic buffer solution.

4. **KClO4**:
- KClO4 (potassium perchlorate) is a salt derived from a strong acid (HClO4) and a strong base (KOH).
- It does not contain a weak acid or a weak base, hence it cannot form a buffer solution.

Based on this analysis, the option that is not a buffer solution is **KClO4**.

### Final Answer:
**KClO4 is not a buffer solution.**