There is "No answer" option.
Can I remove that somehow?
Can I change that to "Unknown"?

Please refer to the manual.

There is "No answer" option. Can I remove that somehow?

Survey setting Show "No answer" - www.limesurvey.org/manual/Survey_setting...ation_.26_navigation

Can I change that to "Unknown"?

Create you own list radio question - www.limesurvey.org/manual/Question_type_-_List_%28Radio%29

Thank you!

No answer is gone.

This Create you own list radio question - manual.limesurvey.org/Question_type_-_List_%28Radio%29 maybe works too,
but I found new easier solution to this. In this new version 2.50+.160426 you can choose that List(radio) type and close&save. Then click this link Warning: You need to add answer options to this question. You can now press Quick add... and type all choices then you can "Save as a label set" and use it all buttons you need