The correct answer is option 4, B.R. Ambedkar. B.R. Ambedkar played a crucial role in drafting the Constitution of India and was the Chairman of the drafting committee. He described the Directive Principles of State Policy as a novel feature of the Constitution.

The Directive Principles of State Policy are a set of guidelines or principles given to the government to provide for the social, economic, and political welfare of the citizens. They aim to promote equality, justice, and the overall development of society. Unlike the fundamental rights, which are justiciable and can be enforced by the courts, the Directive Principles are non-justiciable, meaning they cannot be enforced by the courts. However, they act as a moral and political compass for the government to strive towards achieving the goals mentioned in the Directive Principles.

While Jawaharlal Nehru, Rajendra Prasad, and S.N. Mukherjee were all prominent leaders involved in the framing of the Constitution, it was B.R. Ambedkar who explicitly referred to the Directive Principles as a significant feature of the Constitution.