The second one: You are, if I'm not mistaken, a good person for this experiment.
Explanation:
The first sentence, "You are, if I'm not mistaken a good person, for this experiment." does not have a comma after "mistaken", where there should be one. After "a good person", there should not be a comma.
A.The strangeness of the Looking-Glass world is immediately made known when Alice sees a clock with a living face and chess pieces that move around the room independently.
