`BCl_(3)` is trigonal planar while `AlCl_(3)` is tetrahedral in dimeric state. Explain .

Explanation

To understand why \( BCl_3 \) is trigonal planar while \( AlCl_3 \) is tetrahedral in its dimeric state, we need to analyze the molecular geometry and hybridization of both compounds.

### Step 1: Analyze \( BCl_3 \)
- **Molecular Geometry**: \( BCl_3 \) has a central boron atom bonded to three chlorine atoms. The boron atom has three valence electrons and forms three covalent bonds with chlorine atoms.
- **Hybridization**: The hybridization of boron in \( BCl_3 \) is \( sp^2 \). This means that one \( s \) orbital and two \( p \) orbitals mix to form three \( sp^2 \) hybrid orbitals.
- **Shape**: The three \( sp^2 \) hybrid orbitals arrange themselves in a plane to minimize repulsion, resulting in a trigonal planar shape with bond angles of approximately 120°.

### Step 2: Analyze \( AlCl_3 \)
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