The 42nd Amendment of the Indian Constitution (1976) states that India is a/an __________________ nation.

The correct option is secular.

The Preamble to the Constitution of India serves as a brief introductory statement that sets out the guiding purpose, principles, and philosophy of the document. Under the 42nd Amendment Act of 1976, often referred to as the "Mini-Constitution" due to its vast scope, three new terms were formally added to the Preamble to better define the character of the Indian state: "Socialist", "Secular", and "Integrity".

By incorporating the word "Secular", the amendment explicitly declared India to be a secular nation. This guarantees that the Indian State has no official state religion, treats all religions with equal respect (Sarva Dharma Sambhava), and protects the freedom of belief, faith, and worship for all its citizens.