Final answer:
Twain critiques societal norms by revealing Jim's freedom, emphasizing the absurdity of slavery's social constructs and prompting reflection on society's values.
Step-by-step explanation:
Mark Twain's revelation in the last chapter of Huckleberry Finn that Jim has been a free man throughout most of the novel serves to critique the societal norms and beliefs about slavery and freedom of the time. By showcasing Jim's unnecessary struggles and Huck's moral dilemmas despite Jim's undisclosed freedom, Twain emphasizes the absurdity and cruelty of the social constructs concerning slavery. It calls into question the values and conscience of society, showcasing that the true conflict was not with legal status but with social perception and moral viewpoints.