Oxygen is a non reactive substance. It doesn't form or mix with anything.
Nope oxygen is not radioactive if it was then all humans on earth will be sick with cancer because they breathed in so much radiation from the oxygen.
Yes. Oxygen, being the second most electrognegative element after fluorine, is very reactive.
It reacts easily with other elements. Iron to form rust.
Yes, gold can react with oxygen to form gold oxide.