Who is the protagonist and the antagonist in "The Necklace"?

First of all, do you know what the terms in the question mean? The protagonist is the character the story is centered around, or the main character. In longer stories or novels, there may even be more than one. I like to look at the protagonist as the one who changes or is changed by the events in the story. The antagonist is the person or force that stands in the way of what the protagonist wants or tries to do. Sometimes, the antagonist is the same person as the protagonist, or a part of that person.

In "The Necklace," no-one is working against Madeleine, per se, but her own dissatisfaction with her place in life (or her envy) gets in the way of her happiness. You could say that she is both.