What should happen when the user clicks on the android ‘back’ button

I've been seeing this behavior differently in different apps. Is there any certain navigation axioms related to this? I would like to know which of them is ideal/most preferred.

The application has 5 items in the tab bar (as in the image).

enter image description here

A user navigates through it in the following order: 1 -> 2 -> 3 -> 2 -> 3 . So currently he is on tab 3. The concern is, what should happen when the user clicks on the android 'back' button. The options seen generally are:-

  • Follow the same path in a reverse manner i.e 2 -> 3 -> 2 -> 1
  • Go back to 1 regardless of the path.
  • Exit the app after confirmation.
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