Final answer:
Macbeth's question about Neptune's ocean is an example of hyperbole, highlighting his overwhelming guilt and the sense that not even the largest body of water could cleanse him of his crime.
Step-by-step explanation:
When Macbeth asks, "Will all great Neptune's ocean wash this blood Clean from my hand?" he is employing the literary device known as hyperbole. Hyperbole is an exaggerated statement or claim not meant to be taken literally. In this case, Macbeth is expressing doubt that even the vast waters of Neptune's domain could cleanse his hands of King Duncan's blood, symbolically representing his guilt. This hyperbole underscores the gravity of Macbeth's crime and the psychological impact it has on him.