The correct option stating "Only two statements are correct" is accurate based on an understanding of the Indian Constitution and the relevant laws.

1. Correct: The Central Government does have a duty under Article 356 of the Constitution to protect States against internal disturbances, which reinforces the federal structure and the Union's responsibility to maintain order.

2. Correct: The Constitution provides certain safeguards related to preventive detention; however, it does not explicitly exempt States from providing legal counsel, which is often contentious in practice.

3. Incorrect: While the Prevention of Terrorism Act (POTA) originally limited the admissibility of confessions made to police, this has been contested and revised in courts. In practice, confessions made before police can be considered as evidence under certain circumstances, negating the statement's accuracy.

This understanding aligns with the principles of law and governance in India as covered in standard UPSC sources, reflecting critical elements of constitutional protection, state responsibilities, and procedural law.