Theoretical yield is the maximum amount of product that could be formed from amounts of reactants.
Now, in this problem we will find the theoretical yield of ZnCl2
3.52 mol ZnO x (1 mol ZnCl2 / 1 mol ZnO) = 3.52 mol ZnCl2
18.82 mol HCl x (1 mol ZnCl2 / 2 mol HCl) = 9.41 mol ZnCl2
ZnO is the limiting reactant.
Therefore, we form 3.52 mol of ZnCl2
molar mass of ZnCl2 is
1(65.38) + 2(35.45) = 135.28 g/mol
This has a mass of
m = M x n
m = 135.28 g/mol ZnCl2 x 3.52 mol ZnCl2
m = 476.2 g ZnCl2
Answer: maximum amount of ZnCl2 is 476.2 g
