Using Resolution rule from propositional logic for the xor expression

Question

The XOR operation applied on two propositional Symbols P and Q could be defined as (P or Q) and (Not(P) or Not(Q)) But by using the resolution rule, (P or Q) and (Not(P) or Not(Q)) would result in (Q or Not(Q)), which is always true. I know this is incorrect, but I don't know where I went wrong in this logical deduction.