Introduction:
In a story, the problem or challenge that the characters face is a crucial element as it drives the plot and creates conflict. It is the main obstacle that the characters need to overcome in order to reach a resolution. The placement of this problem or challenge within the story structure is commonly known as the climax.

Explanation:
The climax is the point in the story where the tension and conflict reach their peak. It is the most intense and pivotal moment that determines the outcome of the characters' journey. This is why the problem or challenge that the characters face is typically found at this stage.

Identification:
To identify the climax, it is important to consider the following:

1. Plot Development: The climax usually occurs after the beginning and rising action, where the conflict is gradually introduced and intensified.

2. Turning Point: The climax marks a turning point in the story, where the events and actions lead to a crucial decision or confrontation that will ultimately resolve the conflict.

3. Emotional Intensity: The climax is the most emotionally charged part of the story, where the audience's investment in the characters and their journey is at its peak.

4. Resolution: After the climax, the story moves towards the resolution, where the problem or challenge is addressed and resolved. The resolution provides closure and wraps up the story.

Conclusion:
In summary, the problem or challenge that the characters face in a story is typically located at the climax. This is the point of highest tension and emotional intensity, where the conflict comes to a head and the characters must confront the obstacles in their path. Understanding the placement of the problem within the story structure helps to analyze and appreciate the overall narrative and character development.

The climax is the part of the story where the main problem or challenge faced by the characters reaches its peak. It's a pivotal moment in the narrative.