
Dramatic irony occurs when there is a contradiction between what a character thinks and what the audience knows to be true. Along with the two examples in the above post, there are three other instances of dramatic irony in Act II. In Scene 3 the Friar initially believes that Romeo is still in love with Rosaline and, because he sees that Romeo has been up all night, asks if Rosaline is the reason. He soon learns that it was Juliet who kept Romeo awake.
In Scene 4, Mercutio and Benvolio are also still under the impression that Romeo is hopelessly in love with Rosaline. Mercutio comments,
Alas, poor Romeo, he is already dead,
stabbed with a white wench’s black eye, run
through the ear with a love-song, the very pin of his
heart cleft with the blind bow-boy’s butt shaft.
Good Peter, to hide her face, for her fan’s
the fairer face.

The very first example of dramatic irony occurs in Act 2, scene 1 when Benvolio and Mercutio are looking for Romeo after the Capulet’s party. They are in the Capulet orchard making comments about Romeo’s love for Rosaline. The reason this is dramatic irony is because the audience knows that Romeo is no longer in love with Rosaline; he’s in love with Juliet.
A second example would be in Act 2, scene 2 when Juliet is standing on her balcony. She thinks that she is simply talking to herself about how she feels about Romeo and how she wishes he was not a Montague. Since Romeo is standing right there but she does know it and the audience does, this is dramatic irony.