This riddle is causing a lot of arguments online.
It resembles a question from the game show, Who Wants to Be a Millionaire?
If you choose an answer to this question at random, what is the chance that you will be correct?
Commenters are not only arguing over what the correct answer is, but they are also debating whether it is a puzzle, a riddle, a paradox, or something else entirely.
At the risk of being proven wrong in the comments, I'm going to say there is no correct answer. It's a version of the Epimenides paradox, the same one Captain Kirk used to burn out an android's mechanical brain in "I, Mudd."