Final answer:
The defense mechanism illustrated by a religious leader who attempts to overcome his hidden doubts with intense expressions of spiritual certainty is reaction formation.
Step-by-step explanation:
The defense mechanism illustrated by a religious leader who attempts to overcome his hidden doubts with intense expressions of spiritual certainty is reaction formation. Reaction formation is when someone expresses feelings, thoughts, and behaviors that are opposite to their true inclinations. In this case, the religious leader is expressing strong certainty in an attempt to hide their doubts.
An example of reaction formation would be if a person who dislikes their boss constantly praises and compliments them, even though they truly feel negative towards their boss.
Other defense mechanisms mentioned include projection, regression, displacement, and fixation, but they are not applicable in this scenario.