In what scene does the climax of the novel occur? At the moment of climax, what belief of Winston and Julia's proves to be false?

The climax is Winston's torture with the caged rats. Winston finally gives up Julia. He doesn't just give her up in words, he really believes it. Julia and Winston had agreed that they (the inner party) could never get them to betray each other in their hearts. Both of them do.

"Do it to Julia! Do it to Julia! Not me! Julia! I don't care what you do to her. Tear her face off, strip her to the bones. Not me! Julia! Not me!"