The word "Secular" was inserted in the Preamble of the Indian Constitution by which Amendment?

42nd Amendment

The correct answer is Option 3 - 42nd Amendment

Socialist, Secular and Integrity words were added to the Preamble by the 42nd Constitutional Amendment.

The exact text of the Preamble - 

WE, THE PEOPLE OF INDIA having solemnly resolved to constitute India into a SOVEREIGN SOCIALIST SECULAR DEMOCRATIC REPUBLIC and to secure to all its citizens:

JUSTICE, social, economic and political;

LIBERTY of thought, expression, belief, faith and worship;

EQUALITY of status and of opportunity; and to promote among them all

FRATERNITY assuring the dignity of the individual and the unity and integrity of the Nation;

IN OUR CONSTITUENT ASSEMBLY this twenty-sixth day of November, 1949, do HEREBY ADOPT, ENACT AND GIVE TO OURSELVES THIS CONSTITUTION.