Answer:
a- Her aspirations of an aristocratic rather than a middle class life result in a decline rather than an advancement of social class. an event that occurs that contradicts the expectations of the characters, the readers, or the audience.
b- Maupassant also uses irony, which is when what you expect to happen is the opposite of what actually happens, and this is the driving force behind the surprise ending. It's ironic that the necklace is fake because Mathilde and her husband went into such debt to replace it.
4-The ending shatters that illusion, revealing that the ten years of misery were unnecessary and could have been avoided if only Mathilde had been honest with Madame Forestier.