A question may ask for a way of achieving or explaining something (e.g. A particular set of conditions on a planet, a physical structure, a course of action).
Solutions to the question are based on what would work in reality (or reality with some adjusted parameters). They are objectively valid or invalid, in that they either could our couldn't achieve the desired effect. They ideally should draw on the relevant field of science.
However the effect can be achieved in multiple ways, and the question gives no criteria to rank valid answers. Is it therefore primarily opinion based? (or does that depend on how many possible valid answers there are?)
This question was inspired by this question: Reasons why a Mind Reader would not disclose their abilities , which I feel fits the criteria I have described.