After a Constitution Amendment Bill relating to the Directive Principles of State Policy is passed by the Parliament, what is the next mandatory constitutional step for it to become a law?

The correct answer is President’s Assent.

Under Article 368 of the Constitution of India, a Constitutional Amendment Bill can be introduced in either House of Parliament. Once the bill is passed by both the Lok Sabha and the Rajya Sabha by a special majority (a majority of the total membership of each House and a majority of not less than two-thirds of the members present and voting), it is presented to the President for assent.

The President must give their assent to the bill (as made mandatory by the 24th Constitutional Amendment Act, 1971). After receiving the President’s assent, the bill becomes a Constitutional Amendment Act.

Note: A Constitutional Amendment Bill related to Directive Principles of State Policy (Part IV) does not fall under the provisions of Article 368 that require ratification by at least half of the State Legislatures (which is only required for federal provisions). Furthermore, Supreme Court approval is not a mandatory procedural step in the legislative process, and gazette notification follows after assent.