Question

which one is the most powerful oxidizing element?

Answer 1

FLUORINE IS THE STRONGEST OXIDIZING AGENT

Answer 2

That would mean the most potent electron acceptor. What is the most potent electron acceptor possible. That would probably be a free fluorine atom (excluding the idea of a free heavy atomic nucleus), but free fluorine atoms don't exist in any significant amount in our world outside of a laboratory, nor do free fluorine molecules. There is plenty of free oxygen in our world, so what's around that is more potent than oxygen? After lightning bolts, there is significant amounts of ozone (O3) present, which is probably the most potent oxidizer that can be found in our world. If you look at the whole universe, then probably bare heavy nuclei in the form of cosmic rays would be the answer.