The molecular geometry of SeO3, which has selenium as the central atom surrounded by three oxygen atoms, is trigonal planar. This arrangement occurs because selenium forms three equivalent double bonds with the oxygen atoms.
In a trigonal planar geometry, the bond angles between the atoms are approximately 120 degrees. This geometrical shape is due to the electron pair repulsion theory, which states that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion.
Since SeO3 has no lone pairs on the selenium atom and is symmetric, the bond angles remain ideal at 120 degrees, characteristic of trigonal planar structures. Therefore, SeO3 effectively exemplifies this geometry along with its respective bond angles.