In Mentimeter's presentation view, all the visualizations are optimized for the screen. Therefore, we have set some limits such that the content you input (text, images, etc) does not get too small or crowded out by one another.
Here are the maximum number of answer options for each slide type:
Multiple Choice - 12
100 Points - 12
Scales - 8
2 by 2 Grid - 10
Ranking - 12
As for Content Slides, the recommended maximum number of bullet points is 6.
For Quiz type slides, the maximum number of answer options is 6 so that your audience can see all of them on their smartphone screens.