The pair of compounds that can exist together is :
FeCl3, SnCl2
HgCl2, SnCl2
FeCl2, SnCl2
FeCl3, KI
The pair of compounds that can exist together is FeCl2?, and SnCl2?.
FeCl2? and SnCl2? (both are reducing agents and have lower oxidation no.)
Hence neither can reduce the other.
The correct answer is option 3.