Which molecule has the highest boiling point ?

Options

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

Answer

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

### Step 1: Identify the Molecules
The molecules we are comparing are:
- HI (Hydrogen Iodide)
- HF (Hydrogen Fluoride)
- HBr (Hydrogen Bromide)
- HCl (Hydrogen Chloride)

### Step 2: Understand the Role of Hydrogen Bonding
Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom (like F, O, or N). The strength of hydrogen bonding influences the boiling point of the molecule.

### Step 3: Determine Electronegativity
The electronegativity of the halogens (F, Cl, Br, I) decreases as we move down the group in the periodic table. The order of electronegativity for the halogens is:
- Fluorine (F) > Chlorine (Cl) > Bromine (Br) > Iodine (I)

### Step 4: Analyze Each Molecule
- **HF**: Has strong hydrogen bonding due to the high electronegativity of fluorine.
- **HCl**: Weaker hydrogen bonding than HF because chlorine is less electronegative than fluorine.
- **HBr**: Weaker hydrogen bonding than HCl due to bromine's lower electronegativity.
- **HI**: The weakest hydrogen bonding of the four because iodine has the lowest electronegativity.

### Step 5: Compare Boiling Points
Since hydrogen bonding is strongest in HF due to the high electronegativity of fluorine, it will have the highest boiling point among the four molecules.

### Conclusion
The molecule with the highest boiling point is **HF (Hydrogen Fluoride)**.

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