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 recommended maximum number of answer options, as well as the maximum amount possible, you can set for your questions:
Multiple Choice - 10 (up to 30)
100 Points - 10 (up to 30)
Scales - 6 (up to 8)
2 by 2 Grid - 10 (up to 20)
As for Content Slides, the recommended maximum number of bullet points is 6.
You can still add some more options than those stated above, but keep in mind that your presentation looks best if you follow the guidelines.
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.