To determine in which oxidation state iodine (I) cannot act as a reducing agent, we need to analyze the oxidation states provided: -1, +1, +5, and +7.
### Step-by-Step Solution:
1. **Understanding Reducing Agents:**
- A reducing agent is a substance that donates electrons to another substance, thereby reducing it while itself getting oxidized. This means that for iodine to act as a reducing agent, it must be able to lose electrons.
2. **Electronic Configuration of Iodine:**
- The electronic configuration of iodine is \( [Kr] 5s^2 5p^5 \). This indicates that iodine has 7 valence electrons.
3. **Analyzing Oxidation State -1:**
- In the -1 oxidation state, iodine gains one electron, resulting in the configuration \( 5s^2 5p^6 \). This is a stable, noble gas configuration (similar to xenon). Since it has gained an electron, it cannot lose electrons easily, thus it cannot act as a reducing agent in this state.
4. **Analyzing Oxidation State +1:**
- In the +1 oxidation state, iodine loses one electron. The electron lost will come from the 5s orbital (as it has lower energy than 5p), resulting in the configuration \( 5s^1 5p^5 \). This state is not stable as it is still capable of losing more electrons, but it is not the most favorable for acting as a reducing agent.
5. **Analyzing Oxidation State +5:**
- In the +5 oxidation state, iodine loses a total of 5 electrons. This would involve losing both 5s electrons and 3 from the 5p orbital, leading to a configuration of \( 5p^2 \). In this state, iodine can still act as a reducing agent because it can lose more electrons to achieve a more stable configuration.
6. **Analyzing Oxidation State +7:**
- In the +7 oxidation state, iodine would need to lose 7 electrons. This means all 5s and 5p electrons would be lost, leaving only the d-orbitals. This state is highly unstable and iodine cannot easily lose electrons from the d-orbitals, thus it cannot act as a reducing agent in this state.
### Conclusion:
Iodine cannot act as a reducing agent in the oxidation state of **-1** and **+7**. However, the most definitive answer to the question is that iodine cannot act as a reducing agent in the **+7 oxidation state**.
### Final Answer:
**Iodine cannot act as a reducing agent in the +7 oxidation state.**
---
