Which of the following eqations does not represent a redox reaction?

Which of the following eqations does not represent a redox reaction?
a) ZnCl2 + 2Na —> 2NaCl + Zn
b) 3O2 —> 2O3
c) FeS + Mg —> MgS + Fe
d) Br2 + 2KCl —> 2KBr + Cl2
EXPLAINED ANSWER GOT RATED