Which of the following halogen acids has the highest boiling point ?

Options

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

Answer

To determine which halogen acid has the highest boiling point, we can analyze the boiling points of the common halogen acids: HF (hydrofluoric acid), HCl (hydrochloric acid), HBr (hydrobromic acid), and HI (hydroiodic acid).

### Step-by-Step Solution:

1. **Understanding Boiling Points**: The boiling point of a substance is influenced by the strength of intermolecular forces. The stronger the intermolecular forces, the higher the boiling point.

2. **Types of Intermolecular Forces**:
- Hydrogen bonding is a strong type of dipole-dipole interaction that occurs in molecules where hydrogen is directly bonded to highly electronegative atoms (like F, O, or N).
- Van der Waals forces (or London dispersion forces) are weaker forces that arise due to temporary dipoles in molecules.

3. **Analyzing the Halogen Acids**:
- **HF**: This acid exhibits strong hydrogen bonding due to the presence of fluorine, which is highly electronegative.
- **HCl, HBr, HI**: These acids primarily exhibit Van der Waals forces. The strength of these forces increases with molecular mass:
- HCl has a lower molecular mass than HBr and HI.
- HI has the highest molecular mass among these acids.

4. **Comparing Boiling Points**:
- HF has strong hydrogen bonding, which gives it a higher boiling point compared to the others.
- Among HCl, HBr, and HI, the boiling points increase with molecular mass: HI > HBr > HCl.

5. **Conclusion**:
- HF has the highest boiling point due to hydrogen bonding.
- The order of boiling points is: HF > HI > HBr > HCl.

Thus, the halogen acid with the highest boiling point is **HF (hydrofluoric acid)**.