meaning a divergence from the intense faithfulness he feels for Rosaline, so faithful that he is metaphorically referring to it as a religion.Most ironically, he exclaims, "One fairer than my love? The all-seeing sun / Ne'er saw her match since first the world begun" (I.ii.96-97). However, the reader knows what Romeo does not yet know--that Romeo will fall in love with a woman who returns his affections, and they will both take their lives. Since Rosaline is rejecting Romeo, we know that Rosaline is not the other half of the "pair of star-cross'd lovers [that] take their life" mentioned in the opening prologue (First Prologue.6). The dramatic irony of Romeo's proclamations that none can be more beautiful than Rosaline is even solidified in Scene 5, when Romeo proclaims after seeing Juliet, "Did my heart love till now? Forswear it, sight! / For I ne'er saw true beauty till this night" (I.v.54-55). Hence we see that the moment Romeo declares he could never think of anyone being more beautiful than Rosaline is a perfect example of dramatic irony.

Irony is a very useful literary tool and Shakespeare uses it widely to convey meaning, to warn his characters or his audience, to create humor and to intensify tragedy. There are three main types of irony and dramatic irony occurs when the audience knows something that the characters do not or one character knows something that another does not, something so crucial that it will change the anticipated outcome in terms of what the unsuspecting characters are expecting. In Romeo and Juliet, Romeo and Juliet have no idea that their fate is sealed and yet the audience know right from the beginning; before the action even starts as The Prologue to Act I says, "A pair of star-cross'd lovers take their life..." (6).

Act II begins after Romeo and Juliet meet and each is overwhelmed by his or her feelings for the other. The dramatic irony begins immediately as Romeo comments on what he has overheard Mercutio say. He suggests that Mercutio has never felt the pain of love, referring to "scars" and "a wound," and Romeo thinks that he, unlike his friend, already knows the pain of love. This is an example of dramatic irony as the audience know that the pain Romeo feels now, knowing that Juliet is a Capulet, is nothing compared to the real pain he will feel when, later, he will pay the ultimate price with his life.  

Romeo's reference to the "glove upon that hand" reveals more dramatic irony because Romeo wishes to be so close to Juliet that he is completely reliant on her, such as a glove would be in order to "touch that cheek," (25) and he doesn't realize that his dependence on her will be so complete that he will die after her presumed death. The audience may not yet know how the young lovers will die but the fact that it knows that they will both face the same fate is enough to create the dramatic irony.

There is further dramatic irony in line 70 when Juliet expresses her concern that if Romeo is seen, "they will murder thee" without her knowing that she is as much at risk as he is, as the audience well knows. 

I am going to try to help you, but that which you have identified is the big dramatic irony of the scene. Maybe you are to be breaking it down into parts to create more that one irony???

Dramatic irony occurs when we know something a character doesn't know. We know that both Romeo's friends in the beginning think that Romeo is off looking for Rosaline from the preceding scene. Romeo references this by saying "He jests at scars that never felt a wound." So, we know that Romeo is going after Juliet while the boys think he's out with Rosaline. By the end of the scene, we know that Juliet is hiding from her parents and Nurse. The Nurse doesn't know this when she comes looking for Juliet.

In act 2, scene 4, Mercutio and Benvolio meet in the street, wondering where Romeo is, as they surmise he did not go home the previous night, concluding that a letter delivered to his house included a challenge from Tybalt.

Two aspects of dramatic irony are presented in this scene. The first relates to Romeo’s love. Mercutio jokes that Romeo cannot be killed by Tybalt because he is already dead, meaning that love has symbolically killed him. Mercutio elaborates upon the kinds of wounds that love has made:

Alas, poor Romeo, he is already dead, stabb’d 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. . . .

Mercutio’s comments build directly on what Romeo had said to Friar Lawrence a few minutes earlier, in a riddling reference to Juliet’s family as his “enemy”: “a sudden one hath wounded me / That’s by me wounded.” His two friends are correct to joke about Romeo’s love but wrong to think he was with Rosaline.

In addition, there is dramatic irony, as Mercutio actually predicts his own death. Mercutio foreshadows both Romeo’s death by way of his own. It is Mercutio, not Romeo, who will die at Tybalt’s hand. This killing prompts Romeo to kill Tybalt, not the other way around, which sets in motion the events leading to Romeo’s death.

The irony in this scene is primarily verbal, & the conversation between Benvolio/Mercutio, and later Mercutio/Tybalt is rife with puns and hidden meanings.

Mercutio is portrayed as clever; smart; and a lover of words, puns, and figures of speech. He is able to joke even about death. When Mercutio is asked about his wound, he replies with a pun, a humorous use of a word to suggest two or more meanings, by stating, “No, ’tis not so deep as a well, nor so wide / as a church door; but ’tis enough, ‘twill serve. Ask / for me tomorrow, and you shall find me a grave man.” "Grave" here, of course, serves 2 purposes. It means "serious", but in Mercutio's case, it also means dead. He is, in fact, so witty that no one takes him seriously when he is no longer joking.

The tension is built through the verbal wordplay of the young men. Each insult adds to the audience's anticipation of violence. Once Mercutio has actually been wounded, his verbal play makes the audience continually question if he is truly hurt, or simply joking around. It is the moment of his death which brings the irony home in a fierce way.

In Act 3, Scene 1, Romeo killed Tybalt in order to avenge Mercutio's death. In Act 3, Scene 2, the audience is aware that Juliet's husband is responsible for killing Juliet's cousin, but Juliet herself is not aware of this fact. This set-up is the basis for the dramatic irony in this scene. Dramatic irony occurs when the audience is aware of something that the characters are not aware of. When the nurse bursts in on Juliet's musings wringing her hands in worry, Juliet automatically assumes that something has happened to Romeo. The Nurse, being the comedic character that she is, makes matters worse by crying, "Ah, alas! he's dead, he's dead, he's dead! (line 39)," without specifying who is dead. This in turn makes Juliet even more worried, and she pushes the nurse to tell her more by asking if heaven can truly be so cruel as to take Romeo away from her. Once again, the nurse does nothing to ease Juliet's fears:

Romeo can,Though heaven cannot.Romeo, Romeo!Who ever would have thought it?Romeo! (lines 43-45)

At this point, Juliet is all but convinced that her husband is dead. However, she still has some doubt about her nurse's words and asks her to tell her straight out if Romeo is slain. Alas, the nurse is either too grief-stricken or Shakespeare was having too much fun playing with poor Juliet's emotions, because the nurse not only goes on to vaguely refer to someone's corpse but then makes things worse by throwing Tybalt's name into the mix, "O courteous Tybalt! honest gentleman/That ever I should live to see thee dead! (lines 65-66)"

After so many lines of misunderstanding between Juliet and her nurse, and some amusement or perhaps exasperation experienced by the audience, Juliet asks the nurse, "Is Romeo slaught'red, and is Tybalt dead (line 68)?" At last, the nurse sets the record straight and informs Juliet that Romeo is alive, but banished, and he is banished because he killed Tybalt. Unfortunately, Juliet finds little comfort in finally getting the nurse to straighten out the truth.

Another example of irony is in Romeo's lament before Friar Laurence in Act III:

There is no world without Verona walls,/But Purgatory, torture, Hell itself./Hence banished is banished from the world./And world's exile is death.  The "banished,"/Is death mistermed. III,iii17-21)

There are two instances of irony in Romeo's remarks.  First, he states that it is Purgatory and Hell itself to be outside Verona when within the walls of the city he has been hated all his life by the Capulets, and he has committed an act of murder. 

In another instance, Romeo declares that being banished is "torture and not mercy," but

...Heaven is here,/Where Juliet lives, (III,iii,29)

He thinks that if he could stay in Verona, he would be in "heaven," but he does not know yet that Juliet is so upset over Tybalt's death.

The greatest moment of dramatic irony I can think of between those two scenes occurs as Capulet is making these wedding plans with Paris without Juliet's consent:

I think she will be ruled
In all respects by me; nay, more, I doubt it not.

What makes this ironic is that he thinks he can get his kid to obey and to want the man he wants for her and for a reason she really doesn't care about (Tybalt's death). Capulet doesn't know that Juliet cares for none of this, she feels the exact opposite about all three of these issues.

Much of what happens in Act III, Scene 4 is ironic in this sense.

First of all, Juliet is crying a great deal.  Her family is acting and talking as if she is crying for Tybalt.  Instead, she is crying for Romeo, who killed Tybalt.

Second of all, her family starts to push her to marry Paris.  Although they are doing this, we know that she is already married to Romeo.  This gets to be even more ironic because we know that Juliet is alone in her room with Romeo at the time that her father is giving Paris permission to marry her.

You have certainly chosen a scene fraught with dramatic irony!  Of course, before we begin exploring why this is so, it's always good to review the definition.  Dramatic irony generally occurs when a character thinks one thing, while the reader/audience knows the reality of the situation.  The dramatic irony of this particular scene revolves around Romeo/Juliet and the Lady/Lord Capulet.  When Romeo and Juliet bid each other adieu in this scene they say the following:

Juliet:  O, thinkst thou we shall ever meet again?
Romeo:  I doubt it not; and all these woes shall serve / For sweet discourses in our time to come.
Juliet:  O God! I have an ill-divining soul/Methinks I see thee, now thou art below/As one dead in the bottom of a tomb.

Even if it is an audience member's very first time watching (or reading) Romeo and Juliet, because this is, in fact, a tragedy and because of the indicators given by the chorus, we know that Juliet is right, they will meet again; however, it cannot be amid "sweet discourses" as the two surmise here, but amid despair and sadness.  Further, even upon first reading and perhaps not knowing that Romeo will next be seen by Juliet directly in a tomb, this still can be seen as incredible foreshadowing.

Ironically, much of the dramatic irony in this scene has more to do with Juliet's parents than with Juliet herself. First, Lady Capulet misreads Juliet's tears:

Evermore weeping for your cousin's death? / What, wilt thou wash him from his grave with tears?

Even though the truth comes out a bit later in the scene, here it is clear to the audience that Juliet is pining for Romeo, not Tybalt.

Further, Lord and Lady Capulet are absolutely thrilled with the match of Paris and Juliet.  Juliet's parents plan for her to wed Paris on Thursday!  What we know:  Juliet is already married to Romeo (and she wants a husband named Paris like a hole in her head, pun intended).

The dramatic irony in act 5, scene 3 of Shakespeare's Romeo and Juliet arises from what the audience knows—which is a considerable amount of information—and the characters don't know about each other and about the situation in which they find themselves. Compared to the audience, the characters in the scene know almost nothing, which very much increases the irony in the scene and holds the audience in a heightened state of suspense and anticipation for the entire scene.

The audience knows that Romeo and Juliet are married, the circumstances of the marriage, and everything leading up to this scene, including the fact that Juliet isn't dead but simply in a deep sleep from having taken Friar Laurence's death-simulating sleeping potion.

Paris enters the churchyard where Juliet's tomb is located with the Page. Paris sends the Page off to warn him if anyone else comes into the churchyard. As he strews flowers outside Juliet's tomb, he is unaware that Romeo and Juliet are married, and that Juliet is not dead.

The Page whistles to warn Paris that someone is coming into the churchyard, and Romeo enters with Balthasar as Paris hides. Balthasar is unaware that Romeo and Juliet are married and that Juliet is not dead. Meanwhile, Romeo is unaware that Juliet is not dead.

Romeo give Balthasar a letter for Lord Montague, and Balthasar moves off to the side and falls asleep. Romeo then opens Juliet's tomb, and Paris confronts him, thinking that Romeo intends to defile Juliet's tomb. Romeo doesn't recognize Paris in the dark outside the tomb. Not knowing that he's speaking to Paris, he appeals to Paris not to fight him but doesn't tell him that he's married to Juliet. Paris presses the issue, they fight, and Paris is killed, still unaware that Romeo and Juliet are married, and that Juliet isn't dead.

With his dying breath, Paris asks Romeo to "lay me with Juliet," thinking that he was going to marry Juliet and that therefore he's entitled to lie next to her. Romeo then discovers that he's killed Paris. Romeo lays Paris in the tomb, although not with Juliet. Thinking that Juliet is dead, even though her lips and cheeks are still red and she looks "so fair," he kills himself with the potion he acquired from the Apothecary.

Friar Laurence enters, having no idea what has only recently transpired, thinking that he's going to enter the tomb and wait for Juliet to awaken, and then wait for Romeo to arrive. He doesn't know that Romeo didn't receive the letter that he sent telling him about the sleeping potion. Friar Laurence's heart sinks when he hears from Balthasar that Romeo is already in the tomb, and he's seriously alarmed when he sees the blood outside the tomb.

Friar Laurence enters the tomb just as Juliet wakes up. He hears some noise outside the tomb and urges Juliet to leave the tomb with him, which might have been more successful if he hadn't shown her Romeo and Paris's dead bodies and said that he was going to send her to a cloister of nuns. Seeing Romeo dead, Juliet first tries to take the poison that he took to kill himself, but the vial is empty. She takes his dagger and kills herself with it.

Within minutes, all of Verona is awake and has descended en masse on the churchyard—the Prince, the Chief of the Watch, Lord and Lady Capulet, Lord and Lady Montague, the Page, and everyone else the Page woke up in the middle of the night. Balthasar is found sleeping in the churchyard and brought forward, and the Friar is apprehended trying to run away from the scene.

Of all of those now assembled in the churchyard, only Friar Laurence can explain what's happened. What he tells everyone in the churchyard is everything that the audience already knows. Balthasar also gives the letter that he has from Romeo to the Prince, which supports Friar Laurence's explanation of events.

The extent of the irony in the scene is remarkable, as was Shakespeare's ability to resolve every aspect of Romeo and Juliet's star-crossed relationship in one extraordinary scene.

Dramatic irony is what makes Romeo and Juliet such a poignant play. The audience knows throughout the play that the young lovers will die, because the Chorus says so in the Prologue. But it is in the final scene of the play that the dramatic irony is almost excruciating. Romeo arrives at the Capulet family crypt knowing nothing of the Friar's plot to reunite him with his wife. He believes Juliet is really dead, since the Friar's message to him did not reach him in Mantua. Because the audience knows she is in fact sedated, and not dead, this is an example of dramatic irony. This makes it all the more heartbreaking to witness an utterly heartbroken Romeo committing suicide over his "dead" wife's body. In another bit of dramatic irony, the leaders of both families come to the crypt (along with the Prince) with no knowledge whatsoever of Romeo and Juliet's romance. They do not know what their mutual hatred has done to their children. When the Friar reveals everything, they are so moved that they agree to make amends and to end the old animosity between the two families. The "poor sacrifices of our enmity" redeem their families. The audience knew this would happen too, having been told in the Prologue that "only their children's end...could remove" their "parents' rage."