Give one example of "Much Ado About Nothing" in the play.

Much Ado's main focal point and plot device is the readiness of the characters to accept error and misinformation.  This is a common method of comedy in Shakespeare's plays. Don John's false presentation of Hero is the most important incident in a series of erroneous reports and misunderstandings.  While Don John, the evil brother, and his cohort maliciously mislead their intended victims, Don Pedro benevolently tricks Benedick and Beatrice.  Dogberry is fully capable of confusing himself and everyone else. 

Disguise, another source of error, is also a prominent motif in the play.  At the masque in 2.1, Beatrice and Benedick converse in masks, and their dialogue, more bitter and biting than usual, marks the extreme extent of their hostility.  In the same scene Claudio is pretending to be Benedick when Don John tells him that Don Pedro loves Hero.  More important, the play turns on Margaret's use of a disguise, Hero's clothes, as part of Don John's plot to slander Hero.  The episode is lent futher mystery and confusion by being only reported (in 3.3 by Borachio and in 4.1 by Claudio) and not actually seen on stage.