If I prevent my brother from leaving during a heated argument, what offense am I committing?

The correct answer is unlawful restraint. This offense occurs when a person knowingly restricts another individual's freedom of movement without their consent and without legal justification. In the scenario presented, preventing your brother from leaving during a heated argument constitutes a restriction of his movement.

Unlawful restraint does not require the use of physical force; simply inhibiting someone's ability to leave a space can fulfill the legal criteria for this offense. This scenario demonstrates a clear attempt to control another person's mobility, thereby meeting the definition of unlawful restraint.

While false imprisonment also involves restricting someone's freedom, it typically implies a stronger, more intentional act of confinement. Assault generally refers to causing fear of imminent harmful or offensive contact, while harassment involves unwanted behavior that causes emotional distress, which doesn't directly relate to the act of preventing someone from leaving. Thus, unlawful restraint is the most appropriate designation for the behavior described in the question.