Remember that the configuration of the chiral carbon in the reactant will remain the same untill and unless the hydrogen in the chiral carbon is replaced by hydrogen. But if chlorine attached to that chiral carbon then the configuration may change hence two optical isomers are formed.
Even though in the above two cases there are two chiral centres but only one can change configuration,the other one is fixed.
hence there are a total of 6 products out of which only 4 can be separated through fractional distillation.
Hence the answer is 6,4
Hope it helps
Regards
Piyush Kumar Behera