Which one of the following halogens has the highest bond energy ?

Options

A. `F_2`
B. `CI_2`
C. `Br_2`
D. `I_2`

Answer

To determine which halogen has the highest bond energy, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Halogens**: The halogens include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). These elements belong to Group 17 of the periodic table.

2. **Understand Bond Energy**: Bond energy, or bond dissociation energy, is the amount of energy required to break a bond between two atoms. Higher bond energy indicates a stronger bond.

3. **Trend in Bond Energy**: In general, bond dissociation energy decreases as you move down the group in the periodic table. This is because the atomic size increases, leading to longer bond lengths and weaker bonds.

4. **Analyze Each Halogen**:
- **Fluorine (F)**: Being the smallest halogen, fluorine has a high electronegativity and forms strong bonds. However, due to its small size, the lone pairs on fluorine experience significant repulsion, which weakens the bond.
- **Chlorine (Cl)**: Chlorine is larger than fluorine, and while it has a strong bond, it is weaker than fluorine due to less lone pair repulsion.
- **Bromine (Br)**: Bromine has even larger atomic size, leading to weaker bonds compared to chlorine.
- **Iodine (I)**: Iodine has the largest atomic size among the halogens, resulting in the weakest bond.

5. **Conclusion**: Based on the trend and analysis, chlorine (Cl) has the highest bond energy among the halogens, despite fluorine having a strong bond due to its size and lone pair repulsion.

### Final Answer:
Chlorine (Cl) has the highest bond energy among the halogens.