Question

on first priority & on the first priority which one is correct

Answer 1

I think both are wrong
I'm giving u examples---the safety of the country takes priority over any other matter,
priority is given to traffic already on the roundabout,housework didn't figure high on her list of priorities,etc.
Hope now u understand how to use this word in ur daily life.

Answer 2

i think both are wrong. Eg My study is my prirority