Explanation:

- A.K. Gopalan v. State of Madras was a landmark case in Indian constitutional law.

- In this case, the Supreme Court examined the Preventive Detention Act, 1950.

- The focus was on whether the Act violated fundamental rights guaranteed by the Indian Constitution.

- Specifically, it assessed its compatibility with Article 21, related to personal liberty.

- The relevant section declared ultra vires was Section 14 of the Preventive Detention Act. This section was found vague and excessive, primarily concerning procedure for representation by the detainee.

- Options provided were not sections, but articles.

- Correct Answer: Article 14 - Option 3