The words socialist and secular were inserted in the Preamble to the Constitution by the 42nd Amendment. It is important to note that amendments are changes made to the Constitution. The 16th, 7th, and 44th Amendments did not have any provisions regarding the insertion of the words socialist and secular in the Preamble. Therefore, options 1, 2, and 4 are incorrect.

The 42nd Amendment, also known as the Constitution (Forty-second Amendment) Act, was passed in 1976. It was introduced during the time of the Emergency in India. This amendment brought significant changes to the Constitution, including the addition of the words socialist and secular in the Preamble. These words reflect the values of a socialist and secular country as envisioned by the framers of the Constitution.