In which of the dimerisation process, the achievement of the octet is not the driving force.

Options

A. `2AlCl_3 to Al_2Cl_6`
B. `BeCl_2 to BeCl_2` (solid )
C. `2ICl_3 to I_2Cl_6`
D. `2NO_2 to N_2O_4`

Answer

To determine in which dimerization process the achievement of the octet is not the driving force, we need to analyze the dimerization of different compounds and their electron configurations.

### Step-by-Step Solution:

1. **Understanding Dimerization**: Dimerization is the process where two molecules combine to form a dimer. The driving force for dimerization is often the achievement of a stable electron configuration, commonly the octet rule.

2. **Analyzing AlCl3**:
- In AlCl3, aluminum has 3 valence electrons, and each chlorine has 7 valence electrons.
- When AlCl3 dimerizes, it forms Al2Cl6.
- Each aluminum shares its electrons with chlorine, achieving an octet configuration for all involved atoms.
- Thus, for AlCl3, the achievement of the octet is a driving force.

3. **Analyzing BeCl2**:
- Beryllium (Be) has 2 valence electrons, and chlorine has 7.
- In the solid state, BeCl2 forms a structure where beryllium can accept electrons from chlorine.
- When BeCl2 dimerizes, it also achieves an octet configuration.
- Therefore, for BeCl2, the achievement of the octet is also a driving force.

4. **Analyzing ICl3**:
- Iodine (I) has 7 valence electrons, and chlorine (Cl) has 7.
- In ICl3, iodine can bond with three chlorines. However, iodine can expand its octet, leading to I2Cl6 upon dimerization.
- Here, the driving force is not just the octet but the ability of iodine to expand its octet beyond the typical eight electrons.
- Thus, for ICl3, the achievement of the octet is not the primary driving force.

5. **Analyzing N2O2**:
- In N2O2, nitrogen has 5 valence electrons, and oxygen has 6.
- When N2O2 dimerizes to form N2O4, the nitrogen atoms share electrons with oxygen atoms, achieving a stable configuration.
- Therefore, for N2O2, the achievement of the octet is a driving force.

### Conclusion:
From the analysis, the only dimerization process where the achievement of the octet is not the driving force is the dimerization of **ICl3 to I2Cl6**. This is because iodine can expand its octet beyond the typical eight electrons.