HELLO THERE!
Here are the cases of passiveness for Nitric acid:
When nitric acid (concentrated) is reacted with Iron, Chromium, or Aluminium, they turn passive.
Reason: An insoluble layer of the respective oxides are formed (as nitric acid is a good oxidizing agent) and hence, they prevent any further reaction and hence the material turns passive (inactive).
Way to remove this passivity:
To remove this passivity, the material can be rubbed with sand paper, so that the oxide film gets destroyed.
Also, the passivity can be removed by treating it with strong reducing agents like carbon, hydrogen or carbon monoxide.
THANKS!