Explanation:

- Option 1: Must be proved

- This option is incorrect. S. 25 of the Indian Evidence Act explicitly states that confessions made to a police officer are inadmissible, meaning they don't need to be proved in court.

- Option 2: Need not be proved

- This is the correct option. Confessions made to a police officer are not admissible in court, so there is no requirement to prove them.

- Option 3: Must be proved only in certain cases

- This option is incorrect. There are no standard situations where a confession to a police officer is admissible under S. 25. Other provisions, like S. 27, may apply but don't affect the inadmissibility under S. 25.

- Option 4: Must be proved by that police officer

- This is incorrect. Since the evidence is inadmissible under S. 25, there's no need for anyone to prove it, including the police officer.

Option 2: Need not be proved is correct.