The situational irony which occurs in “The Colomber” by Dino Buzzati is that the colomber pursues Stefano in order to give him a magic pearl. Option D is correct,
Stefano gave up his dream of becoming a sea captain seeking to ensure that he will live a long life after seeing the Colomber.
Tthe Colomber was considered a harbinger of Death and that whoever sees it will be doomed for life.
However, the reason why the Colomber was after Stefano was that it had to give Stefano a pearl that would grant him good luck and success in life. And the irony lies on the fact that Stefano feared the Colomber was false and baseless.