The correct answer is option 1, which is the "Right to privacy." It is not explicitly mentioned as a fundamental right in the Constitution of India. However, the Supreme Court of India has interpreted Article 21 of the Constitution, which guarantees the right to life and personal liberty, to include the right to privacy. The court has ruled that the right to privacy is inherent in the fundamental rights enshrined in the Constitution, making it a fundamental right.

Option 2, "Equality before law," is explicitly mentioned in Article 14 of the Constitution, and it grants every person equality before the law and equal protection of the laws. Option 3, "Abolition of untouchability," is mentioned in Article 17, which specifically prohibits untouchability and its practice in any form. Option 4, "Right to form associations or unions," is mentioned in Article 19(1)(c), which guarantees the right to form associations or unions.

Therefore, the right that is not expressly mentioned as a fundamental right in the Constitution but has been articulated by the Supreme Court as a fundamental right is the "Right to privacy."