The correct option is C The SN1 reaction involves the complete inversion of the configuration of the optically active substrate
In SN1 reaction mechanism, formation of carbocation is the rate determining step.
Thus,
Rate of reaction∝stability of carbocation
Carbocation stability increases as tertiary > secondary > primary.
The nucleophile is not involved in the RDS in SN1 reaction. Thus it does not affect the rate of SN1 reaction.
Rate of the reaction ∝[R−X]1[Nu]0
Formed carbocation is sp2 hybridised and the nucleophile can attack from both the sides which leads to 50% inversion of configuration and 50% retention of configuration. This 50-50 mixture of d and l configuration leads to racemic mixture of products.
But practically, inversion of configuration is little bit higher than 50% and retention of configuration is little bit lower than 50% due to the hindrance of leaving group. So the product will be partial racemisation.
Hence, incorrect statement is (b).