Situational irony is when what happens is different or the complete opposite of what one might expect or would be usual in a given situation. Thus, there are two steps involved in creating situational irony: setting up an expectation for the reader, then breaking that expectation with something unexpected.

In "Lamb to the Slaughter," Roald Dahl sets up the readers' expectations of what kind of person Mary is when he describes her:

Mary Maloney was waiting for her husband to come home from work. Now and again she glanced at the clock, but without anxiety: She merely wanted to satisfy herself that each minute that went by made it nearer the time when he would come home. ... For her, this was always a blissful time of day. She knew he didn't want to speak much until the first drink was finished, and she was satisfied to sit quietly, enjoying his company after the long hours alone in the house. She loved to luxuriate in the presence of this man, and to feel—almost as a sunbather feels the sun—that warm male glow that came out of him to her when they were alone together.

Mary is a devoted housewife who dotes on her husband. She cares deeply for his comfort and finds time spent with him "blissful." However, things change after her husband shocks her with the news that he is leaving her:

[Mary] simply walked up behind him and without any pause she swung the big frozen leg of lamb high in the air and brought it down as hard as she could on the back of his head.

By killing her husband, Mary performs an action that is inconsistent with the image the reader has of her character and personality, resulting in situational irony. Following her murderous act, Mary surprises readers once more, as she suddenly, with a now "clear" mind, puts together an alibi for herself, primarily concerned for the safety and future of her unborn child. Mary's cool and calculated behavior for the remainder of the story is just as—if not more—surprising than her crime.

What is an example of dramatic, situational, and verbal irony in "Lamb to the Slaughter" by Roald Dahl?

Dramatic irony occurs when the audience or reader of a work of literature knows something the characters don't. In the case of "Lamb to the Slaughter," the audience knows what the police do not: that Mary clobbered and killed her husband with the leg of lamb that they are eating for dinner.

Situational irony happens when events don't work as expected in a story. In this case, Mary awaits her husband Patrick eagerly and happily at the start of the story and thinks of nothing more than how she can dote on him. She is heavily pregnant and expects to have a happy family and domestic life with her husband and new baby as the future unfolds. Ironically, however, her husband tells her is going to divorce her. This situation is the opposite of her life expectations.

There are a number of instances of verbal irony in the story. Verbal irony occurs when a statement means the opposite of what people think. One example is when Mary says "It'd be a favor to me if you'd eat it [the lamb] up." The officers think it is because it is what her husband would have wanted and because she doesn't wish the meal to go to waste. Ironically, however, it's a favor to her for reasons they never suspect: they are eating the murder weapon.

What is an example of dramatic, situational, and verbal irony in "Lamb to the Slaughter" by Roald Dahl?

There are many examples of irony in "Lamb to the Slaughter," but the penultimate line of the story is exceptional in providing examples of situational, dramatic and (arguably) verbal irony all at once. The line is:

Probably right under our very noses. What you think, Jack?

The situational irony here could scarcely be stronger: the policemen are eating the evidence for which they have been searching so assiduously. The dramatic irony is similarly strong: the reader knows how Mary's husband was killed and shares her amusement at the unintentional aptness of the policeman's comment.

Finally, there is an unusual variety of verbal irony in the phrase "right under our very noses." This is not sarcasm, since the policeman does not intend to be ironic, but he uses what is intended to be a non-literal phrase with ironic exactness. When we say something is right under our noses, we mean it is in plain sight, not that it is literally immediately beneath the nose. The mouth, however, is literally beneath the nose and the officers have been chewing the murder weapon as they discuss its absence.

There are, of course, more traditional examples of verbal irony in the story, including the title, which suggests that the lamb is a sacrificial victim rather than a bludgeon.

What is an example of dramatic, situational, and verbal irony in "Lamb to the Slaughter" by Roald Dahl?

I have had to edit your question down to focus on one question alone - multiple questions are not allowed under enotes regulations.

In this excellent short story the biggest kind of irony that is at work is situational irony. Consider how Mary Maloney is presented as the perfect wife in the opening paragraphs - she loves her husband deeply and waits upon him hand and foot:

She loved to luxuriate in the presence of this man, and to feel - almost as a sunbather feels the sun - that warm male glow that came out of him to her when they were alone together.

How surprising and unexpected, then, that the next minute she kills the object of her affection.

Dramatic irony is of course also present when we and Mary know that the police are actually eating the murder weapon whilst they are talking about looking for it:

"Personally I think it's right here on the premises."

"Probably right under our very noses."

Of course, the dramatic irony is that the police are right - for they are consuming it.

Lastly, verbal irony is also evident when Mary Maloney asks the policemen to do her a "small favour." Obviously, this isn't a "small favour" - it is actually a massive favour so she can commit the perfect murder and never be charged with what she has done.

Dahl is a master of irony and we can clearly see the three types of irony in operation in this excellent short story.

How is irony used in "Lamb to the Slaughter" by Roald Dahl?

The main irony of the story is that a meek and mild housewife becomes a murderer—and not just any murderer, but a murderer who expertly covers her tracks and gets away with her crime. In general terms, all of the numerous ironies of the story point toward a role reversal, which is itself ironic. The policemen investigating the crime don't suspect Mary of carrying out this brutal killing. They're still operating under the sexist assumption that Mary, as a loyal and faithful housewife, is simply incapable of such a thing. Detectives are supposed to be inherently suspicious, to go where the evidence leads them and not to assume anything. Yet when it comes to Mary, all that goes by the board, and their sexist assumptions, which had previously kept Mary in a state of subordination, give her a sense of power and control for the first time in her life.

How is irony used in "Lamb to the Slaughter" by Roald Dahl?

Irony is one of the most commonly employed literary techniques in "Lamb to the Slaughter." It is ironic, for example, that the main character, Mary, is described early on as having "placid eyes," but she then goes on to murder her husband—the very antithesis of being placid.

Moreover, Patrick's request that Mary does not cause any "problem" for him in the divorce is given an ironic twist by the very fact of his murder. Mary's use of the leg of lamb as a murder weapon is also ironic when the meat that was designed to nourish Patrick is instead used to end his life.

In a final twist, Mary feeds this leg of lamb to the policemen who come to investigate Patrick's death; they sit in her home, with mouths "full of meat," and have no idea they are eating the murder weapon they are so keen to discover.

By employing irony in this way, Dahl adds an element of dark humor to his story and suggests Mary might just get away with murder.

Why does the author Roald Dahl use verbal and dramatic irony in the short story "Lamb to the Slaughter"?

Dramatic irony is when the spectator or reader knows something one or more of the characters do not. In this case, the reader knows that Mary has killed her husband and is trying to get away with it. The police, doctors, and photographer have no clue. Dahl keeps the reader in suspense in this way. The reader waits anxiously to see if Mary will get away with the murder. It is interesting that some (maybe most) readers will root for Mary without realizing they are rooting for a murderer. With the detectives unaware of the fact that they are eating the evidence they are looking for, the story develops into a dark comedy. The irony is so rich (pun on being rich and tasty), it is unbelievable to the point of absurdity. 

Verbal irony is when a statement's actual meaning is different from what is expressed. Verbal irony tends to be intentional. For example, when someone says that a window is as clear as mud, he/she means that it is dirty, not clear. But verbal irony can also be unintentional. If the auditor/reader/spectator discerns a meaning other than what is expressed, this also qualifies as verbal irony. In one of the last lines, one of the investigators, speaking of the evidence, says to Jack, "It's probably right under our noses." He means this figuratively; he means to say that the weapon is probably somewhere easy to find. He is correct, but he has no idea that the meat they are eating was the murder weapon. He has no idea that the evidence is literally under their noses as they eat it. This example of verbal irony is used for dark comedic effect.