This question tests the understanding of 'illusion'. An illusion is something that appears real but is not; therefore, it is a mistaken impression or belief. Option A, 'a true perception' is the opposite of an illusion. B, 'a mistaken impression' aligns perfectly with the meaning of illusion. Option C, 'a factual statement' is true and hence is not an illusion. Option D, 'a confirmed reality' is also opposite of an illusion.The critical part is that an illusion deceives the senses, it is a false appearance or belief. The correct answer is B.