Which one of the following cannot be estimated by`l_2`?

Options

A. `SnCl_2`
B. `Cu^(2+)`
C. `Na_2S_2O_3`
D. `H_2S`

Answer

To solve the question of which species cannot be estimated by `I2`, we will analyze the behavior of the given compounds with respect to iodine.

### Step-by-Step Solution:

1. **Identify the Compounds**: The question provides a list of four compounds. Among them, we need to identify which one cannot reduce iodine (`I2`) to iodide (`I^-`).

2. **Understanding the Reaction**: Iodine can be reduced to iodide by certain reducing agents. A reducing agent donates electrons and gets oxidized in the process. We need to find out which of the given compounds cannot act as a reducing agent for iodine.

3. **Analyze Each Compound**:
- **Cu²⁺ (Copper Ion)**: This ion cannot reduce iodine to iodide. Instead, it can oxidize iodide ions to iodine. Therefore, it does not serve as a reducing agent for iodine.
- **Na₂S₂O₃ (Sodium Thiosulfate)**: This compound can reduce iodine to iodide. The reaction is as follows:
\[ \text{I}_2 + \text{Na}_2\text{S}_2\text{O}_3 \rightarrow \text{2NaI} + \text{Na}_2\text{S}_4\text{O}_6 \]
- **Other Compounds**: Without specific names, we can assume that other reducing agents (like certain metals or other compounds) can also reduce iodine to iodide.

4. **Conclusion**: Since Cu²⁺ cannot reduce iodine to iodide and instead oxidizes iodide to iodine, it is the only species among the given options that cannot be estimated by `I2`.

### Final Answer:
The species that cannot be estimated by `I2` is **Cu²⁺**.

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