`BCl_(3)` exists as monomer whereas `AlCl_(3)` is dimerised through halogen bridging. Give reason, Explain the structre of the dimer of `AlCl_(3)` also.

Explanation

### Step-by-Step Solution:

1. **Understanding the Molecular Structure of BCl₃**:
- Boron trichloride (BCl₃) is a molecule where boron is bonded to three chlorine atoms.
- Boron has three valence electrons and forms three covalent bonds with chlorine, resulting in a trigonal planar geometry.
- Importantly, boron does not have any vacant d-orbitals in its valence shell (2s² 2p¹), which limits its coordination number to 3. Therefore, BCl₃ exists as a stable monomer.

2. **Understanding the Molecular Structure of AlCl₃**:
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