Which of the following is considered a defense in criminal law?

Insanity is recognized as a formal defense in criminal law, specifically indicating that a defendant was unable to understand the nature of their actions or differentiate right from wrong due to severe mental illness at the time the crime was committed. This defense can lead to a verdict of not guilty by reason of insanity, which suggests that the defendant cannot be held criminally responsible for their actions due to their psychological state.

In contrast, judgment, personal gain, and financial hardship do not constitute legal defenses. Judgment might reflect a decision-making process but does not absolve one from criminal liability. Personal gain refers to a motivation behind actions, which, in a criminal context, typically aggravates rather than mitigates criminal behavior. Financial hardship likewise does not serve as a defense in criminal cases; it is merely a circumstance and does not impact the legal liability for committing a crime. Therefore, insanity stands out as a legally recognized defense in the context of criminal law.