Answer: d-orbitals account for the sulphur- oxygen double bond.
Explanation:
Looking at the nature of bonding in SOCl2, the sulphur is bonded to two chlorine atoms and one oxygen atom. The sulphur has a lone pair of electrons. There are four bonds and four electron pairs if we don't count the lone pair on sulphur. This leads to a tetrahedral shape. However, if we invoke a valence state in which d orbitals are involved and the thionyl chloride is still sp3 hybridized, then we will have one electron in the d-orbital which overlaps with a 2p electron from oxygen to form the double bond. The four sp3 orbitals accommodate eight electrons including the lone pair on sulphur while the d-orbital accommodates the remaining two electrons from the pi-bond thereby completing the ten electrons. The approach of canonical structures and charge separation shown in the image attached
