The pair of compounds that cannot exist together is
(i) $FeC{l}_3,SnC{l}_2$
(ii) $HgC{l}_2,SnC{l}_2$
(iii) $FeC{l}_2,SnC{l}_2$
(iv) $FeC{l}_3,KI$

The correct option is C (i), (ii) and (iv) only
Solution:- (C) (i), (ii) and (iv) only

The compounds with lower oxidation number and which cannot be reduced by one another can exist together. Thus $Fe{Cl}_2$ and $Sn{Cl}_2$ can exist together as ${Fe}^{2+}$ cannot be reduced by ${Sn}^{2+}$.