Among halogen acids (hydrogen halides) ….. Is the strongest reducing agent

Answer

To determine which hydrogen halide is the strongest reducing agent, we can analyze the properties of the hydrogen halides (HF, HCl, HBr, HI) based on their thermal stability and dissociation energies.

### Step-by-Step Solution:

1. **List the Hydrogen Halides**:
The hydrogen halides we are considering are HF (hydrogen fluoride), HCl (hydrogen chloride), HBr (hydrogen bromide), and HI (hydrogen iodide).

**Hint**: Remember that hydrogen halides are formed from hydrogen and halogens.

2. **Understand Thermal Stability**:
The thermal stability of hydrogen halides decreases as we move down the group in the periodic table. This means that HF is the most stable, while HI is the least stable.

**Hint**: Consider how bond strength changes as you go from HF to HI.

3. **Evaluate Ionization and Dissociation Energies**:
- HF has the highest bond strength and dissociation energy, making it the least likely to donate electrons.
- HI has the lowest bond strength and dissociation energy, meaning it can more easily lose electrons.

**Hint**: Lower dissociation energy indicates that the bond is weaker and can break more easily, facilitating electron donation.

4. **Identify the Strongest Reducing Agent**:
A reducing agent is a substance that donates electrons in a chemical reaction. Since HI has the lowest dissociation energy, it can lose electrons more readily than the other hydrogen halides, making it the strongest reducing agent among them.

**Hint**: Think about which substance can most easily undergo oxidation by losing electrons.

5. **Conclusion**:
Therefore, the strongest reducing agent among the hydrogen halides is HI.

### Final Answer:
**HI (hydrogen iodide) is the strongest reducing agent among the hydrogen halides.**