Its 25%. The rules of answering a question with a set of options is that you may only choose one and only one is right unless explicitly stated otherwise. Anything else is breaking the rules, which as the taker would be disqualifying. If you start narrowing it down, as in "its 25% and theres two so now i need to guess therefore its 50" you are no longer answering the question at random and you have answered wrong. But you do have to make that coin flip. Good luck.