Following reaction (s) is /are involved in the iodometric estimation

Options

A. `Cr_(2)O_(7)^(2-) +H^(+)+I^(-) to 2Cr^(3+)+I_(2),I_(2)+S_(2)O_(3)^(2-)toS_(4)O_(6)^(2-)+I^(-)`
B. `MnO_(4)^(-)+H^(+)+I^(-) toMn^(2+)+I_(2),I_(2)+S_(2)O_(3)^(2-)toS_(4)O_(6)^(2-)+I^(-)`
C. `MnO_(4)^(-)+OH^(-)+I^(-)to MnO^(2)+I_(2),I_(2)+S_(2)O_(3)^(2-) to S_(4)O_(6)^(2-)+I^(-)`
D. `Cr_(2)O_(7)^(2-)+OH^(-)+I^(-) to 2Cr^(3+)+I_(2),I_(2)+S_(2)O_(3)^(2-)toS_(4)O_(6)^(2-)+I^(-)`

Answer

To solve the question regarding the reactions involved in iodometric estimation, we will break down the process into clear steps.

### Step-by-Step Solution:

1. **Understanding Iodometric Titration**:
- Iodometric titration is a redox titration that involves the oxidation of iodide ions (I⁻) to iodine (I₂) by a strong oxidizing agent.

2. **First Reaction**:
- The first step involves a strong oxidizing agent, such as potassium dichromate (K₂Cr₂O₇) or potassium permanganate (KMnO₄), which reacts with iodide ions in a neutral or slightly acidic medium.
- For example, the reaction can be represented as:
\[ \text{Cr}_2\text{O}_7^{2-} + 6 \text{I}^- + 14 \text{H}^+ \rightarrow 2 \text{Cr}^{3+} + 3 \text{I}_2 + 7 \text{H}_2\text{O} \]
- Here, iodide ions are oxidized to iodine.

3. **Second Reaction**:
- The liberated iodine (I₂) is then titrated with sodium thiosulfate (Na₂S₂O₃), commonly referred to as hypo.
- The reaction can be represented as:
\[ \text{I}_2 + 2 \text{S}_2\text{O}_3^{2-} \rightarrow 2 \text{I}^- + \text{S}_4\text{O}_6^{2-} \]
- In this step, iodine is reduced back to iodide ions.

4. **Conclusion**:
- Therefore, the reactions involved in iodometric estimation include the oxidation of iodide ions to iodine by a strong oxidizing agent and the reduction of iodine back to iodide ions by sodium thiosulfate.

### Final Answer:
The reactions involved in iodometric estimation are:
- A: The reaction of iodide ions with a strong oxidizing agent in an acidic medium.
- B: The titration of liberated iodine with hypo (sodium thiosulfate).