To determine which AB molecule is trigonal pyramidal, let’s analyze the structure of each molecule in the list:
1. NH₃ (Ammonia):
- The nitrogen atom in NH₃ has five valence electrons.
- It forms three bonds with hydrogen atoms, using three of its valence electrons.
- This leaves one lone pair of electrons on the nitrogen atom.
- The presence of the lone pair creates a repulsion that pushes the bonded hydrogen atoms down, resulting in a trigonal pyramidal shape.
2. CO₂ (Carbon Dioxide):
- The carbon atom in CO₂ has four valence electrons.
- It forms two double bonds with two oxygen atoms.
- There are no lone pairs of electrons on the carbon atom.
- The resulting structure is linear, not trigonal pyramidal.
3. SO₃ (Sulfur Trioxide):
- The sulfur atom in SO₃ has six valence electrons.
- It forms three double bonds with three oxygen atoms.
- Like CO₂, there are no lone pairs of electrons on the sulfur atom.
- The resulting structure is trigonal planar, not trigonal pyramidal.
After analyzing the structures, we conclude that:
- NH₃ is the molecule that has a trigonal pyramidal shape due to the lone pair of electrons on the nitrogen atom.
Therefore, the answer to the question is NH₃.
