Out of all halogen hydracids, the weakest is:

Options

A. HI
B. HBr
C. HF
D. HCl

Explanation

To determine which halogen hydride is the weakest acid, we can analyze the acidic strength of the halogen hydrides: HF (hydrogen fluoride), HCl (hydrogen chloride), HBr (hydrogen bromide), and HI (hydrogen iodide).

### Step-by-Step Solution:

1. **Understanding Acidic Strength**:
The acidic strength of a compound generally increases with the ability to release H⁺ ions. In the case of halogen hydrides, the bond strength between H and the halogen atom plays a crucial role.

2. **Bond Strength Consideration**:
The bond strength of H-X (where X is a halogen) decreases as we move down the group in the periodic table. This is because the size of the halogen increases, leading to a longer and weaker bond between H and the halogen.

3. **Order of Bond Strength**:
The bond strengths can be ranked as follows:
- HF > HCl > HBr > HI
This means that HF has the strongest bond and HI has the weakest bond.

4. **Acidic Character Order**:
The acidic character increases as the bond strength decreases. Therefore, the order of acidic strength is:
- HI > HBr > HCl > HF
This indicates that HI is the strongest acid and HF is the weakest acid.

5. **Conclusion**:
Based on the above analysis, we conclude that the weakest halogen hydride (or halogen acid) is HF (hydrogen fluoride).

### Final Answer:
The weakest halogen hydride is **HF (hydrogen fluoride)**.