Which one of the following does not have a pyramidal shape?

Options

A. `P(CH_(3))_(3)`
B. `(CH_(3))_(3)N`
C. `P(SiH_(3))_(3)`
D. `(SiH_(3))_(3)N`

Answer

To determine which of the given compounds does not have a pyramidal shape, we will analyze the molecular geometry of each compound listed: tri-methylphosphine, tri-methylamine, tri-silile phosphine, and tri-silile amine.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- Tri-methylphosphine (P(CH₃)₃)
- Tri-methylamine (N(CH₃)₃)
- Tri-silile phosphine (SiH₃)₃P
- Tri-silile amine (SiH₃)₃N

2. **Determine the Hybridization:**
- **Tri-methylphosphine (P(CH₃)₃):**
- Phosphorus (P) is bonded to three methyl groups and has a lone pair.
- Hybridization: sp³
- Geometry: Pyramidal shape due to the presence of a lone pair.

- **Tri-methylamine (N(CH₃)₃):**
- Nitrogen (N) is bonded to three methyl groups and has a lone pair.
- Hybridization: sp³
- Geometry: Pyramidal shape due to the presence of a lone pair.

- **Tri-silile phosphine ((SiH₃)₃P):**
- Phosphorus (P) is bonded to three silane groups and has a lone pair.
- Hybridization: sp³
- Geometry: Pyramidal shape due to the presence of a lone pair.

- **Tri-silile amine ((SiH₃)₃N):**
- Nitrogen (N) is bonded to three silane groups.
- Hybridization: sp² (due to back bonding with silicon)
- Geometry: Planar shape (not pyramidal) because of sp² hybridization.

3. **Conclusion:**
- Among the given compounds, tri-silile amine (SiH₃)₃N does not have a pyramidal shape; it is planar due to sp² hybridization.

### Final Answer:
The compound that does not have a pyramidal shape is **tri-silile amine (SiH₃)₃N**.

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