What is the hybridisation of carbon in transition state in SN2 mechanism?
In transition state of SN2 mechanism, the carbon atom is $\ce{sp^2}$ hybridised due to its planar structure. At this point, carbon almost acquires 'pentavalency' with three full bonds and two 'partial' bonds, and a planar complex is formed, which is $\ce{sp^2}$ hybridised.