When $I_2$   is reacts with the mixture of KF, KCl, KBr then the products formed are respectively

Because  is the weakest oxidising agent, it cannot replace $B{r}_2,C{l}_2$   (or) $F_2$  in  $KBr,KCl$  (or) $KF$ . Hence $I_2$  is passed through  $KF,KCl,KBr$  mixture, no reaction takes place