What is situational irony? How does Antony show it at the end of the play?
Your question concerning Shakespeare's Julius Caesar is complex, and sometimes determining types of irony used can be difficult and can force one to make decisions along a fine line, so to speak. Also, your question is a little vague. I'm assuming you're referring to Antony's final speech, in which he praises Brutus as noble, pointing out that Brutus assassinated Caesar because he thought it was the best thing for Rome, unlike the other conspirators.
Situational irony involves a difference or an incongruity between expectation and reality, and derives from events or situations, not from statements made by a character.
Thus, Antony's words do not in themselves constitute situational irony. They may, however, further reveal and highlight the situational irony present throughout the play: that actions stemming from noble motives and a noble cause can lead to an ignoble ending, to tragic consequences.
It is ironic that although Brutus acts because of reasons that are noble, he causes a civil war and ends up dead, as do many others. His motives are pure, but the results are tragic. If expectations are that noble Brutus will be victorious, the reality is that he isn't. Antony doesn't directly state the irony (he states only that Brutus was different from the other conspirators), but that is irrelevant. Characters do not have to be aware of situational irony.
Related to the above is Brutus's thinking that his ability to judge people and to make decisions is good enough to pull off the assassination and maintain power. His misjudgments and poor decisions recur frequently in the play. He thinks--he has expectations--that he is a good judge of character, and a good decision maker. Others think so, too. The reality is that he is neither. Nobility and pure motives are not enough. Brutus thinks he can lead the conspiracy to victory. But he doesn't.