The fact that okonkwo finds himself isolated from the clan as he returns from exile is an example of

The answer is tragic irony. Tragic irony is otherwise known as dramatic irony. This irony can be seen in very nearly all of the classic dramas categorized as tragedies. In those dramas, the author often allows the reader, or audience, to identify more about a situation than the characters. Thus, tragic irony creates inaptness between what a character does or says and what the reader knows to be true. Often this incidence is very tragic, leading to the collapse of the character while the audience helplessly looks on.

the answer to "what does the narrator realize by the end of the story" is b.