The correct answer is option 1: Article 15. Article 15 of the Indian Constitution states that there should be no discrimination on grounds of caste, religion, race, sex, or place of birth. This article ensures that every citizen is treated equally and prohibits any form of discrimination by the state or any private individual or organization. It is a fundamental right that is essential for maintaining social equality and justice. Option 2, Article 21, protects the right to life and personal liberty, but does not specifically address discrimination. Option 3, Article 25, guarantees the freedom of religion and does not directly relate to discrimination. Option 4, Article 30, relates to the right of minorities to establish and administer educational institutions and is not directly related to the prohibition of discrimination.