Stereoisomers

First pair: cannot be superimposed on its partner.
Second pair: cannot be superimposed on its partner.
Third pair: can be superimposed on its partner.


From the second set of molecules:

First pair: enantiomers and therefore also stereoisomers
Second pair: these are the same molecule!
Third pair: not stereoisomers.
Fourth pair: enantiomers and therefore also stereoisomers.


Third set of molecules:

First molecule:S
Second molecule: S


For molecules based around a central carbon atom, for enantiomers to be possible, all the four substituents on the carbon atom must be different.