Final answer:
Hamlet's mordant sarcasm is displayed in Act II as he interacts with Polonius and Horatio.
Step-by-step explanation:
An instance of Hamlet's mordant sarcasm can be seen in Act II of the play, when Hamlet interacts with Polonius and Horatio. During their conversation, Polonius dismisses the idea of ghosts, calling them figments of the imagination. In response, Hamlet sarcastically remarks that he knows for a fact that a majority of people have encountered spirits, regardless of whether their intentions were wicked or charitable.