Which one of the following Articles of the Indian Constitution provides that ‘It shall be the duty of the Union to protect every State against external aggression and internal disturbance’?

The correct answer is Article 355. This article is part of the Emergency Provisions under Part 18 of the Indian Constitution. It explicitly assigns two duties to the Union government: first, to protect every state against external aggression and internal disturbance, and second, to ensure that the government of every state is carried on in accordance with the provisions of the Constitution. Briefly, the other options are incorrect because Article 215 relates to High Courts being courts of record, Article 275 deals with grants from the Union to certain States, and Article 325 states that no person shall be ineligible for inclusion in an electoral roll on grounds of religion, race, caste, or sex.