Option 1 (morale) -> refers to confidence or enthusiasm of a group, not the lesson of a story.
Option 2 (amoral) -> means lacking moral sense; it's an adjective describing someone unconcerned with right/wrong.
Option 3 (moral) -> the lesson or principle taught by a story; fits perfectly in "the moral of the story."
Option 4 (iniquitous) -> means grossly unfair or wicked; an adjective that doesn't fit this context.
Hence, Option 3 (moral) -> "The moral of the story" is the standard idiomatic expression used to describe the lesson or teaching that can be learned from a narrative -> correct