observe the given reaction, n−Butane→hυCl2, the total number of mono-chloro products (Including stereo isomers) which are possible in this reaction.

1-Chloro butane and 2-chloro butane are the two structure isomers obtained.  But  2-chloro butane contains chiral carbon, hence it can give rise to two isomers. Totally 3 isomers.