Which of the following solutions does not change its colour on passing ozone through it ?

Options

A. starch iodide solution
B. alcohlic solution of benzidien
C. acidic solution of potassium dichromate
D. acidified solution of `FeSO_(4)`

Explanation

To solve the question of which solution does not change its color on passing ozone through it, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Ozone as an Oxidizing Agent**:
- Ozone (O3) is known to be a strong oxidizing agent. This means it has the ability to oxidize certain substances, which can lead to a change in color of the solution.

2. **Analyzing Starch Iodide Solution**:
- The starch iodide solution contains iodide ions (I-). When ozone is passed through this solution, it oxidizes I- to I2 (iodine), which results in a color change (the solution turns blue-black due to the formation of the starch-iodine complex).
- **Conclusion**: This solution changes color.

3. **Analyzing Alcoholic Solution of Benzidine**:
- Benzidine is an organic compound that can also undergo oxidation. When ozone is passed through an alcoholic solution of benzidine, it reacts and changes color.
- **Conclusion**: This solution changes color.

4. **Analyzing Acidic Solution of Potassium Dichromate (K2Cr2O7)**:
- Potassium dichromate is a strong oxidizing agent where chromium is in its maximum oxidation state (+6). Since it cannot be oxidized further, it does not react with ozone.
- To confirm, we can calculate the oxidation state of chromium:
\[ 2 \times \text{(oxidation state of K)} + 2 \times \text{(oxidation state of Cr)} + 7 \times \text{(oxidation state of O)} = 0 \]
\[ 2 \times 1 + 2X + 7 \times (-2) = 0 \implies 2 + 2X - 14 = 0 \implies 2X = 12 \implies X = +6 \]
- Since chromium is already in its highest oxidation state, there will be no reaction with ozone, and thus no color change.
- **Conclusion**: This solution does not change color.

5. **Analyzing Acidified Solution of FeSO4**:
- Iron (II) sulfate (FeSO4) contains Fe²⁺ ions. When ozone is passed through this solution, it oxidizes Fe²⁺ to Fe³⁺, resulting in a color change from pale green (Fe²⁺) to yellow/brown (Fe³⁺).
- **Conclusion**: This solution changes color.

### Final Answer:
The solution that does not change its color on passing ozone through it is the **acidic solution of potassium dichromate (K2Cr2O7)**.