which of the following hydrogen bond is strongest in vapour phase ?

Options

A. `HF………..Hf`
B. `HF………….HCl`
C. `HCl………….HCl`
D. `Hl…………..HF`

Answer

To determine which hydrogen bond is the strongest in the vapor phase among the given options (HF, HCl, and HBr), we can follow these steps:

### Step 1: Understand Hydrogen Bonding
Hydrogen bonding occurs when a hydrogen atom covalently bonded to a highly electronegative atom (like F, O, or N) interacts with another electronegative atom. The strength of hydrogen bonds is influenced by the electronegativity of the atoms involved.

### Step 2: Identify the Electronegativity of Atoms
- **Fluorine (F)**: Electronegativity = 4.0
- **Chlorine (Cl)**: Electronegativity = 3.0
- **Bromine (Br)**: Electronegativity = 2.8

From this, we can see that fluorine is the most electronegative element among the three.

### Step 3: Analyze the Compounds
- **HF (Hydrogen Fluoride)**: Contains hydrogen bonded to fluorine, which is highly electronegative.
- **HCl (Hydrogen Chloride)**: Contains hydrogen bonded to chlorine, which is less electronegative than fluorine.
- **HBr (Hydrogen Bromide)**: Contains hydrogen bonded to bromine, which is the least electronegative of the three.

### Step 4: Compare the Strength of Hydrogen Bonds
Since HF has the hydrogen atom bonded to the most electronegative atom (fluorine), it will form the strongest hydrogen bond. In contrast, HCl and HBr will have weaker hydrogen bonds due to the lower electronegativity of chlorine and bromine, respectively.

### Conclusion
Based on the analysis, the strongest hydrogen bond in the vapor phase is found in HF.

### Final Answer
The strongest hydrogen bond in the vapor phase is in **HF**.

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