The 'climax' of a plot is what happens-

Correct answer: at the peak of tension or the turning point of the play.

• Climax:
- Climax is the highest point of tension in a narrative’s plot.
- It’s the most exciting moment.
- Often, the climax is also when the main problem of the story is faced and solved by the main character or protagonist.
- The rising action leads up to the climax, and then (after the climax) follows the falling action.
- অর্থাৎ, এটি হচ্ছে কোন নাটকের বা গল্পের সর্বোচ্চ অবস্থা বা turning point যেখানে ঘটনার বৃদ্ধি শেষ হয় আর ঘটনার পতন শুরু হয়।
- সুতরাং, Climax happens at the height of a plot.

Source:
1. Britannica
2. An ABC of English Literature by Dr. M. Mofizar Rahman.