Answer : To balance a chemical equation you need to find the same number of molecules on both the sides of the reaction.
Here in the reaction ;
![KI + Pb (NO_(3))_(2)----\ \textgreater \ Pb I_(2) + KNO_(3)](https://img.qammunity.org/2019/formulas/chemistry/high-school/ldvg3nu44x4ve0ptqz26h6ps0vpwk0edza.png)
here we can see that I is not balanced so we need to balance that,
also nitrate is unbalanced we need to work on that as well.
so on solving we get,
![2KI + Pb (NO_(3))_(2)----\ \textgreater \ Pb I_(2) + 2KNO_(3)](https://img.qammunity.org/2019/formulas/chemistry/high-school/p57zec5bv92vppypb66uddaad4ulvpl1t0.png)