Final answer:
The type of irony present when Mary intends to cook a good meal for her husband, unaware of potential tragedy, is dramatic irony. This occurs when the audience knows something the character does not.
Step-by-step explanation:
The type of irony used as Mary returns home from the grocery store with the intention of cooking a good meal for her tired husband, unaware of potential tragedy, is dramatic irony. This is because the reader or audience is aware of something significant that the character does not know, creating a situation where the character's words or actions have a different meaning for the audience than they do for the character. In the context given, it sounds like a dark event has occurred or is about to occur that Mary is oblivious to, yet the audience is likely aware, setting up a classic case of dramatic irony.