Step 1: The M'Naghten or right-and-wrong test asks whether unsoundness of mind robbed the accused of the ability to know the nature or wrongfulness of the act.
Step 2: Indian criminal law incorporates this principle as a statutory defense of insanity.
Step 3: The relevant provision is Section 84 of the IPC, which states that nothing is an offence done by a person who, by reason of unsoundness of mind, is incapable of knowing the nature of the act or that it is wrong or against the law.
Step 4: Hence the correct citation is IPC Section 84, not any CrPC section or IPC 48.
\[\boxed{\text{IPC 84}}\]