Final answer:
John's action of keeping the money found in a wallet is an example of the defense mechanism of rationalization, specifically the 'Denial of Responsibility', as he justifies his actions by blaming the owner's carelessness.
Step-by-step explanation:
John's behavior of keeping the $350 he found in a wallet and justifying it by blaming the owner for losing the wallet is an example of a defense mechanism known as rationalization. Rationalization occurs when a person justifies or excuses their behavior with plausible but not necessarily true reasons. In this situation, John is denying responsibility for his actions by suggesting that the wallet owner's carelessness justifies his decision to keep the money. This method of reducing guilt and anxiety showcases the Denial of Responsibility, a specific type of rationalization, which is a common ego defense mechanism.