The space model which is obtained by joining the points representing various bonded atoms gives the shape of the molecule. The geometry of the molecule is definite relative arrangement of the bonded atoms in a molecule. The shape and geometry of a molecule is explained by valence shell electron pair repulsion theory given by Gillespie and Nyholm.
Which is not the electron geometry of covalent molecules ?

Options

A. Pentagonal bipyramidal
B. Octahedral
C. Hexagonal
D. Tetrahedral

Answer

To determine which option is not an electron geometry of covalent molecules, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Electron Geometry**: Electron geometry refers to the spatial arrangement of electron pairs around a central atom in a molecule. This includes both bonding pairs (shared between atoms) and lone pairs (not shared).

2. **Identify the Given Options**: The options provided are:
- A) Pentagonal bipyramidal
- B) Octahedral
- C) Hexagonal
- D) Tetrahedral

3. **Analyze Each Option**:
- **A) Pentagonal bipyramidal**: This geometry is associated with sp³d³ hybridization and is a valid electron geometry for some covalent molecules.
- **B) Octahedral**: This geometry corresponds to sp³d² hybridization and is also a valid electron geometry for covalent molecules.
- **C) Hexagonal**: This geometry is not commonly recognized as an electron geometry in the context of covalent bonding. It does not correspond to any standard hybridization state.
- **D) Tetrahedral**: This geometry is associated with sp³ hybridization and is a valid electron geometry for covalent molecules.

4. **Conclusion**: Based on the analysis, the option that is not an electron geometry of covalent molecules is **C) Hexagonal**.

### Final Answer:
The correct answer is **C) Hexagonal**.

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