No, to be precise it's not infinite and not guaranteed to be free of repetition. However, DBPedia holds ~15 million entities corresponding to Wikipedia article

No, to be precise it's not infinite and not guaranteed to be free of repetition. However, DBPedia holds ~15 million entities corresponding to Wikipedia articles. Although only a fraction of those can be used for quiz questions (many don't have labels or their potential quiz answers don't have labels etc.), the chance to get a duplicate is still pretty low.