Which one of the following hydrogen halides has the lowest boilling point ? .

Options

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

Answer

To determine which hydrogen halide has the lowest boiling point among HF, HCl, HBr, and HI, we can follow these steps:

### Step 1: Identify the Compounds
We have four hydrogen halides to consider:
- HF (Hydrogen Fluoride)
- HCl (Hydrogen Chloride)
- HBr (Hydrogen Bromide)
- HI (Hydrogen Iodide)

### Step 2: Understand the Role of Hydrogen Bonding
Hydrogen bonding significantly affects boiling points. HF exhibits strong hydrogen bonding due to the high electronegativity of fluorine. This leads to a higher boiling point compared to the other hydrogen halides.

### Step 3: Compare HCl, HBr, and HI
The remaining compounds (HCl, HBr, and HI) do not exhibit hydrogen bonding because chlorine, bromine, and iodine are less electronegative than fluorine. Instead, their boiling points are influenced by Van der Waals forces.

### Step 4: Analyze the Trend in Boiling Points
As we move down the group from HCl to HI, the size of the halogen increases. Larger atoms lead to stronger Van der Waals forces, resulting in higher boiling points. Therefore, the order of boiling points for these compounds is:
- HI > HBr > HCl

### Step 5: Conclusion
From our analysis, we can conclude that HCl has the lowest boiling point among the hydrogen halides listed.

### Final Answer
The hydrogen halide with the lowest boiling point is **HCl**.

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