Quote a line in the seventh scene in Hamlet that develops the theme of appearance vs. reality.
Your question was a little vague since it is usually required to name the Act and Scene numbers in order to locate a particular scene in the play. However, the seventh scene in the play would be Act II, Scene ii (since Act One has five scenes), and since it is a very long and significant scene, I decided to go with that.
Please re-enter your question (giving both Act and scene numbers) if you meant to refer to another scene.
There are many moments in this scene that deal with appearance versus reality -- the entrance of Hamlet pretending to be mad, the underhanded visitation of Rosencrantz and Guildenstern-- but I will focus on Hamlet's response to the performance given by one of the players.
He asks one of the players to perform some lines that have special significance to him, and then, once he is alone with the audience, he marvels at how an actor could become so consumed with emotion for a fictitious event, while he, Hamlet has such a cause in real life and can do nothing:
What's Hecuba to him, or he to her,
That he should weep for her? What would he do
Had he the motive and the cue for passion
That I have? He would drown the stage with tears,
And cleave the general ear with horrid speech...
A dull, and muddy-mettled rascal, peak
Like John a-dreams, unpregnant of my cause,
And can say nothing.
Hamlet goes on to berate himself for what he should be doing and expounding on his cowardice. It is this speech that leads him to decide to expose the reality of Claudius' guilt by presenting before him a play that demonstrates his murder of Hamlet Senior.