A key piece of information that foreshadows the outcome of the story and is shared in the exposition of "The Story of an Hour" is

that Mrs. Mallard has struggled with mental illness

that Mr. Mallard works for the railroad

that Richards is a close friend of the family

that Mrs. Mallard has a heart condition

A key piece of information that foreshadoes the outcome of the story and is shared in the exposition of "The Story of an Hour" is D) that Mrs. Mallard has a heart condition.

Explanation:

"The Story of an Hour" is a short story written by author Kate Chopin. Readers are told at the beginning of the narrative that the main character, Mrs. Mallard, has a heart condition. That's why she cannot be scared or surprised; it could be fatal to her. That key piece of information serves as foreshadow for the story's outcome: Mrs. Mallard indeed dies due to her heart condition.

In the story, some evidence leads Mrs. Mallard's sister and a friend of theirs to believe that Mrs. Mallard's husband is dead. They are very careful when letting her know the terrible news, since they do not wish for her to die from her heart condition. However, in an ironical twist, Mrs. Mallard does not die from the shock of her husband's death. She is undoubtedly sad, but soon recovers her spirits when she realizes she is about to be free. That she will no longer have to account for her actions. The shock that kills her comes when she sees her husband, safe and sound, coming into the house.

That Mrs. Mallard has a heart condition is stated in the very first sentence of the story, foreshadowing the outcome of her death. It isn't the news that her husband has died that upsets her, but the news that he is alive that causes her death after the joy of knowing to be free.