What is the dramatic irony in this passage?

The audience knows that Nora and Doctor Rank are having an affair, but Nora denies it.
The audience knows that Mrs. Linde is jealous of Nora, but Nora does not know this.
The audience knows that Krogstad loaned Nora money, but Mrs. Linde does not know this.
The audience knows that Doctor Rank loaned Nora money, but Nora denies this.