Which of the following is responsible strach-iodide paper blue when it is brought in contact with `O_(3)`?

Options

A. Liberation of iodine
B. Liberation of oxygen
C. Formation of alkali
D. Reaction of ozone with litmus paper.

Explanation

To solve the question of which substance is responsible for turning starch-iodide paper blue when it comes in contact with ozone (O3), we can follow these steps:

### Step 1: Understand the Reaction
Ozone (O3) is a strong oxidizing agent. When it comes in contact with iodide ions (I⁻) present in starch-iodide paper, it can oxidize these iodide ions.

**Hint:** Remember that ozone is known for its oxidizing properties.

### Step 2: Write the Reaction
The reaction that occurs when iodide ions react with ozone in the presence of water can be represented as follows:

\[ 2 I^- + O_3 + H_2O \rightarrow I_2 + O_2 + 2 OH^- \]

In this reaction:
- Iodide ions (I⁻) are oxidized to form iodine (I2).
- Ozone (O3) is reduced to oxygen (O2).
- Hydroxide ions (OH⁻) are also produced.

**Hint:** Focus on the products of the reaction to understand the color change.

### Step 3: Identify the Color Change
The formation of iodine (I2) is crucial because iodine reacts with starch to form a blue-black complex. This is the reason why the starch-iodide paper turns blue when it comes in contact with ozone.

**Hint:** Recall the color change that occurs when iodine interacts with starch.

### Step 4: Conclusion
The blue-black color observed on the starch-iodide paper is due to the liberation of iodine (I2) from the reaction between iodide ions and ozone.

**Final Answer:** The correct option is the liberation of iodine, which causes the starch-iodide paper to turn blue-black.

### Summary of Steps:
1. Recognize that ozone is an oxidizing agent.
2. Write the balanced chemical equation for the reaction.
3. Identify the formation of iodine as the cause of the color change.
4. Conclude that the liberation of iodine is responsible for the blue-black color.