Which of the following is an example of a defense used in criminal cases involving mental capacity?

The example of a defense used in criminal cases involving mental capacity is the insanity defense. This defense asserts that a defendant was unable to understand the nature of their actions or distinguish right from wrong due to a severe mental disorder at the time the crime was committed. The focus here is on the individual's mental state, which serves as a basis for claiming that they should not be held criminally responsible for their actions.

The insanity defense examines the mental capacity of a person at the time of the crime, exploring whether their cognitive functions were impaired due to mental illness, thus impacting their ability to form the requisite intent to commit a crime. Successful use of this defense may lead to a verdict of not guilty by reason of insanity, which has significant implications for the individual, often resulting in treatment rather than incarceration.

While infancy is a defense that addresses the concept of age and legal responsibility, and self-defense relates to justifying the use of force, they do not fall under the same category of mental capacity-related defenses. Therefore, insanity is the appropriate and primary example in the context of mental capacity defenses in criminal law.