Answer
(a)$2Li+Cl_2\rightarrow 2LiCl$
(b)$2K+F_2\rightarrow 2KF$
(c)$2Na+I_2\rightarrow 2NaI$
Work Step by Step
(a)Li reacts with $Cl_2$ to form LiCl(Li lose an electron and Cl gain an electron):
$Li+Cl_2\rightarrow LiCl$ (balance Cl by having $1Cl_2$ as reactant and 2LiCl as product)
$Li+Cl_2\rightarrow 2LiCl$ (balance Li by having 2Li as reactant and 2LiCl as product)
$2Li+Cl_2\rightarrow 2LiCl$
(b)K reacts with $F_2$ to form KF(K loses an electron and F gains an electron):
$K+F_2\rightarrow KF$ (balance F by having $1F_2$ as reactant and 2KF as product)
$K+F_2\rightarrow 2KF$ (balance K by having 2K as reactant and 2KF as product)
$2K+F_2\rightarrow 2KF$
(c)Na reacts with $I_2$ to form NaI(Na loses an electron and I gain an electron):
$Na+I_2\rightarrow NaI$ (balance I by having $1I_2$ as reactant and 2NaI as product)
$Na+I_2\rightarrow 2NaI$ (balance Na by having 2Na as reactant and 2NaI as product)
$2Na+I_2\rightarrow 2NaI$
