To determine the electronic geometry of a molecule, we need to consider the number of electron pairs around the central atom. In the case of sulfite, the sulfur atom is the central atom. It has three oxygen atoms bonded to it and one lone pair of electrons. This gives a total of four electron pairs around the sulfur atom.
According to VSEPR theory, four electron pairs around a central atom adopt a tetrahedral arrangement. However, in the case of sulfite, one of the electron pairs is a lone pair. Lone pairs take up more space than bonding pairs, so they cause the tetrahedral arrangement to be distorted. This results in a trigonal pyramidal electronic geometry.
The molecular geometry of sulfite is also trigonal pyramidal. This is because the molecular geometry is determined by the arrangement of the atoms, and the atoms are arranged in a trigonal pyramidal shape in order to minimize the repulsion between the electron pairs.
