Hi James,
There are 2 problems in your "logic".
1- In pure logic/linguistics "Select all of the true statements from the list below:" pre-supposes that at least one statement is true. I would argue that if you word your instruction that way and none of the choices is in fact correct then you are misleading your students.
2. The way the moodle quiz module works, you cannot expect the "correct solution" to a question to be the absence of any answer. If the "correct answer" were "no ticks", and the student did not tick any choice, then that response would be marked as wrong by the program. If you do want a "no answer" possibility, you should enter it as the last choice, i.e.
Grass is blue.Blue is green.
Henry VIII is alive and well.
Father Christmas and the Easter Bunny are best friends.
I can see the green shoots of economic recovery.
None of those.
Hope that helps,
Joseph
PS.- I have no idea what you mean by "2^5 possible answers..."