In a school book it is written
Dramatic Irony or Irony of situation: It involves a situation in a play or story in which the audience knows the reality which the speaker or character is ignorant of.
Shakespeare’s tragedies, Macbeth and Hamlet abound in scenes which provide good examples of dramatic irony.
As far as my reading of Macbeth is concerned, I couldn’t find anything like “which the audience knows the reality which the character is ignorant of”. The scene where Macbeth hallucinates and sees Banquo sitting at the feast could be called “which the audience knows the reality ….” but it isn’t that ironical (because for me something is ironical if it involves the opposite of what is being said or expected) and Lady Macbeth and others quite aware of reality. Can someone please explain what the book’s author had in mind when he made such a statement that Macbeth was a good example of dramatic irony?