In the reaction,
`I_(2)+2S_(2)O_(3)^(2-) rarr 2I^(-)+S_(4)O_(6)^(2-)`.

Options

A. `I_(2)` is reducing agent.
B. `I_(2)` is oxidising agent and `S_(2)O_(3)^(2-)` is reducing agent
C. `S_(2)O_(3)^(2-)` is oxidising agent.
D. `I_(2)` is reducing agent and `S_(2)O_(3)^(2-)` is oxidising agent.

Explanation

To determine the reducing and oxidizing agents in the reaction:

\[ \text{I}_2 + 2 \text{S}_2\text{O}_3^{2-} \rightarrow 2 \text{I}^- + \text{S}_4\text{O}_6^{2-} \]

we will follow these steps:

### Step 1: Identify the oxidation states of the elements involved.

1. **Iodine (I)** in \(\text{I}_2\) has an oxidation state of 0 (elemental form).
2. **Iodine (I)** in \(\text{I}^-\) has an oxidation state of -1.
3. **Sulfur (S)** in \(\text{S}_2\text{O}_3^{2-}\):
- Let the oxidation state of sulfur be \(x\).
- The equation for the oxidation state is:
\[ 2x + 3(-2) = -2 \implies 2x - 6 = -2 \implies 2x = 4 \implies x = +2 \]
- So, sulfur in \(\text{S}_2\text{O}_3^{2-}\) has an oxidation state of +2.
4. **Sulfur (S)** in \(\text{S}_4\text{O}_6^{2-}\):
- Let the oxidation state of sulfur be \(y\).
- The equation for the oxidation state is:
\[ 4y + 6(-2) = -2 \implies 4y - 12 = -2 \implies 4y = 10 \implies y = +2.5 \]
- So, sulfur in \(\text{S}_4\text{O}_6^{2-}\) has an oxidation state of +2.5.

### Step 2: Determine the changes in oxidation states.

- **Iodine**:
- Changes from 0 (in \(\text{I}_2\)) to -1 (in \(\text{I}^-\)).
- This indicates that iodine is **gaining electrons** and is therefore **reduced**.

- **Sulfur**:
- Changes from +2 (in \(\text{S}_2\text{O}_3^{2-}\)) to +2.5 (in \(\text{S}_4\text{O}_6^{2-}\)).
- This indicates that sulfur is **losing electrons** and is therefore **oxidized**.

### Step 3: Identify the oxidizing and reducing agents.

- Since iodine is gaining electrons and being reduced, it acts as the **oxidizing agent**.
- Since sulfur is losing electrons and being oxidized, it acts as the **reducing agent**.

### Conclusion:
- **Oxidizing Agent**: \(\text{I}_2\)
- **Reducing Agent**: \(\text{S}_2\text{O}_3^{2-}\)