The shape of the SO3 (sulfur trioxide) molecule is trigonal planar.
This can be understood by considering the VSEPR (Valence Shell Electron Pair Repulsion) theory, which explains the geometry of molecules based on the number of electron pairs surrounding a central atom. In the case of SO3, the sulfur atom is the central atom bonded to three oxygen atoms.
Since there are three bonding pairs and no lone pairs of electrons on the sulfur atom, the electron pairs will arrange themselves to be as far apart from each other as possible to minimize repulsion. This arrangement leads to a trigonal planar configuration, where the bond angles are approximately 120 degrees.
In summary, the absence of lone pairs and the presence of three double bonds in the SO3 molecule causes it to adopt a trigonal planar shape.