ISSUE:

Hello everyone, I had a question regarding the epoxidation stereochemistry, I wanted to ask you if the third molecule is the same as the other two, and if it is not the case, I do not understand why the epoxide of the other stereochemistry would be formed, or if it would give racemic mixture
Another doubt, the reason why the first two molecules are identical is because they have the same absolute configuration, when applying the Cahn-Ingold and Prelog rule?

Hello Elena, all the molecules you have drawn are exactly the same molecule in different projections and the molecule you have drawn is not chiral, remember that the presence of one or more carbons with 4 different substituents (stereogenic center) is not sufficient or necessary for a molecule is chiral.