Unfortunately I had to radically alter your original question, which actually consisted of many different separate questions. Please remember that you are only allowed to ask one question when using enotes, not multiple questions. I have edited your question to ask a general question about this excellent short story. In responding to it, I will refer to the irony in this tale.
One of the notable characteristics of this story is its final line:
When the doctors came they said she had died of heart disease--of joy that kills.
Here we see that the sickness affecting Mrs. Mallard that is referenced in the first sentence of the tale is returned to in the final sentence. And yet here, the meaning is completely different and richly ironic. Of course, it is the unexpected appearance of her husband that is responsible for Mrs. Mallard's death, yet, on one level, it was not the joy of seeing him again that resulted in her demise. On the contrary, what Mrs. Mallard experiences after hearing the news of her husband's death is a kind of awakening that makes her savour her "freedom" and release from the constricting institution of marriage:
There would be no one to live for her during those coming years; she would live for herself. There would be no powerful will bending hers in that blind persistence with which men and women believe they have a right to impose a private will upon a fellow-creature.
Thus, the true cause of her death is the savouring of this "freedom" that her future now promises her only to have that "freedom" cruelly and suddenly revoked. It is this shock that kills her, although everyone else believes, ironically, that she died because of her joy at seeing her husband alive.