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

Options

A. Starch iodide solution
B. Alcoholic solidium of benzidine
C. Acidic solution of `FeSO_4`
D. Acidified solution of `K_2Cr_2O_7`

Explanation

To solve the question of which solution does not change its color upon passing ozone through it, we will analyze the given options step by step.

### Step 1: Understand the nature of ozone
Ozone (O₃) is a strong oxidizing agent. When it comes into contact with certain solutions, it can oxidize the components of those solutions, leading to a color change.

### Step 2: Analyze the options
We have the following solutions to consider:
1. Starch iodide solution
2. Alcoholic sodium of benzidine
3. Acidic solution of FeSO₄
4. Acidified solution of K₂Cr₂O₇

### Step 3: Evaluate each solution
- **Starch iodide solution**: When ozone is passed through this solution, it oxidizes iodide ions (I⁻) to iodine (I₂), which will change the color of the solution from colorless to brown.

- **Alcoholic sodium of benzidine**: This compound can also undergo oxidation, which may lead to a color change.

- **Acidic solution of FeSO₄**: Ozone can oxidize Fe²⁺ to Fe³⁺, resulting in a color change from pale green to yellow.

- **Acidified solution of K₂Cr₂O₇**: In this case, K₂Cr₂O₇ contains chromium in the +6 oxidation state. Ozone cannot oxidize chromium further than this state. Therefore, there will be no reaction, and the color will remain unchanged.

### Step 4: Conclusion
Based on the analysis, the solution that does not change its color upon passing ozone through it is the **acidified solution of K₂Cr₂O₇**.

### Final Answer
The correct option is **D. Acidified solution of K₂Cr₂O₇**.

---