Section 84 of the Indian Penal Code, 1860 provides the defence of unsoundness of mind. Which of the following correctly describes what must be established to successfully invoke this defence?

Section 84 of the IPC provides a complete defence to criminal liability but it recognises only legal insanity, not medical insanity. The distinction is critical: a person may be medically diagnosed as mentally ill and yet not qualify for the Section 84 defence if they retained cognitive understanding of their act. The section requires that at the exact time of committing the act, the accused must have been incapable of either (i) knowing the nature of the act, or (ii) knowing that what they were doing was either wrong or contrary to law. The impairment of cognitive faculty must be total, not partial partial derangement that does not obliterate the knowledge of right and wrong does not suffice. The burden of proving the defence of unsoundness of mind lies on the accused on a balance of probabilities. The Supreme Court in Jai Lal v. Delhi Administration (1969) held that there is a legal presumption of sanity, and the accused must rebut it with positive evidence.