Arrange the hydrogen halides in decreasing order of their reducing power.

Explanation

To arrange the hydrogen halides (HF, HCl, HBr, HI) in decreasing order of their reducing power, we need to consider the bond strength of the HX bonds (where X is a halogen). The reducing power is determined by the ability of these compounds to donate protons (H⁺ ions), which is influenced by the strength of the bond between hydrogen and the halogen.

### Step-by-Step Solution:

1. **Understand Reducing Power**:
- Reducing power refers to the ability of a substance to donate protons (H⁺ ions). The weaker the HX bond, the easier it is for the compound to lose a proton, indicating higher reducing power.

2. **Identify the Hydrogen Halides**:
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