Final answer:
In Kate Chopin's "The Story of an Hour", Mrs. Mallard experiences the realization and recognition of her freedom while sitting in her comfortable chair, which is the 'thing' that overtakes her.
Step-by-step explanation:
The "thing" that overtakes Mrs. Mallard as she sits in her comfortable chair by the window is B. the realization/recognition of her freedom. In Kate Chopin's "The Story of an Hour", Mrs. Mallard initially feels shocked by the news of her husband's death, but soon she is overcome with the sense of freedom his passing grants her. The narrative describes her as experiencing a sense of release and newfound independence as she comprehends the life she will lead free from the constraints of her marriage.