Final answer:
The literary device used in the title 'A Good Man is Hard to Find' is irony, as it suggests an incongruity between appearances and reality, particularly in the context of the story's dark themes. Option C is the correct answer.
Step-by-step explanation:
The literary device used in the title A Good Man is Hard to Find is irony. Irony is a rhetorical device where the actual meaning is different from the literal meaning or the expectations of the audience are somehow thwarted, usually in juxtaposing ways.
The title indicates that it might be a mere observation about the challenges of finding decent people, but considering the events of the story and Flannery O'Connor's often dark themes, it might be read as a commentary on the morally corrupt, flawed nature of humanity and the elusive nature of goodness. The commonlit story plays with themes of goodness and evil in unexpected ways, which underpins the ironic interpretation of the title.
None of the other given options - simile, metaphor, and alliteration - are present in the title, as the phrase does not use 'like' or 'as', it doesn't compare two unlike things directly, and it doesn't involve repetition of initial consonant sounds.