The enthalpy of dissociation (in kJ/mol) of fluorine, chlorine, bromine and iodine are :

Options

A. 239.7, 190.2, 155, 148.95
B. 148.95, 155, 190.2, 239.7
C. 239.7, 155, 190.2, 148.95
D. 155, 239.7, 190.2, 148.95

Explanation

To solve the question regarding the enthalpy of dissociation of fluorine, chlorine, bromine, and iodine, we need to understand the concept of bond dissociation energy and how it varies among these halogens.

### Step-by-Step Solution:

1. **Identify the Molecules**:
The molecules we are considering are diatomic molecules of the halogens:
- Fluorine (F₂)
- Chlorine (Cl₂)
- Bromine (Br₂)
- Iodine (I₂)

2. **Understand Bond Dissociation Energy**:
The bond dissociation energy is the energy required to break a bond in a molecule, resulting in the formation of two separate atoms. The higher the bond dissociation energy, the stronger the bond.

3. **Trends in the Halogens**:
- As we move down the group in the periodic table (from fluorine to iodine), the size of the atoms increases due to the addition of electron shells.
- Larger atomic size leads to longer bond lengths, which generally results in weaker bonds and lower bond dissociation energies.

4. **Consider the Effects of Atomic Size**:
- **Fluorine (F₂)**: Smallest size, but has significant inter-electronic repulsions due to its small atomic radius and lone pairs, making it less stable and resulting in a lower bond dissociation energy.
- **Chlorine (Cl₂)**: Larger than fluorine, with a higher bond dissociation energy than fluorine.
- **Bromine (Br₂)**: Larger than chlorine, with a lower bond dissociation energy than chlorine.
- **Iodine (I₂)**: Largest size, resulting in the weakest bond and the lowest bond dissociation energy.

5. **List the Enthalpy of Dissociation Values**:
Based on the trends and the understanding of bond strengths, we can list the approximate bond dissociation energies for these molecules:
- Chlorine (Cl₂): 239.7 kJ/mol
- Bromine (Br₂): 190.2 kJ/mol
- Fluorine (F₂): 155 kJ/mol
- Iodine (I₂): 148.95 kJ/mol

6. **Final Arrangement**:
The order of bond dissociation energies from highest to lowest is:
- Cl₂: 239.7 kJ/mol
- Br₂: 190.2 kJ/mol
- F₂: 155 kJ/mol
- I₂: 148.95 kJ/mol

### Conclusion:
The enthalpy of dissociation for the halogens is as follows:
- Chlorine (Cl₂): 239.7 kJ/mol
- Bromine (Br₂): 190.2 kJ/mol
- Fluorine (F₂): 155 kJ/mol
- Iodine (I₂): 148.95 kJ/mol