Which of the following has lowest boiling point

Options

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

Answer

To determine which of the following elements has the lowest boiling point among fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), we need to analyze the trends in boiling points of the halogens.

### Step-by-Step Solution:

1. **Identify the Group**:
- Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I) are all members of Group 17 (the halogens) in the periodic table.

**Hint**: Remember that elements in the same group have similar properties but show trends in physical properties like boiling points as you move down the group.

2. **Understand the Trend in Boiling Points**:
- As you move down the group from fluorine to iodine, the atomic size increases due to the addition of electron shells. This increase in size generally leads to an increase in boiling points.

**Hint**: Think about how larger atoms can have stronger London dispersion forces due to their greater number of electrons.

3. **Consider Intermolecular Forces**:
- The boiling point of a substance is influenced by the strength of its intermolecular forces. In the case of halogens, the primary intermolecular forces are London dispersion forces, which increase with increasing atomic size and mass.

**Hint**: Recall that larger molecules have more electrons and can form stronger temporary dipoles, leading to higher boiling points.

4. **Compare the Boiling Points**:
- Fluorine (F) has the smallest atomic size and mass among the halogens, resulting in the weakest London dispersion forces. Therefore, it has the lowest boiling point.
- Chlorine (Cl), Bromine (Br), and Iodine (I) have progressively higher boiling points due to their larger sizes and stronger intermolecular forces.

**Hint**: Look up the boiling points of each halogen to see the numerical values and confirm the trend.

5. **Conclusion**:
- Based on the analysis, fluorine (F) has the lowest boiling point among the given halogens.

**Final Answer**: Fluorine (F) has the lowest boiling point.