The correct answer is option 1: Jawaharlal Nehru. Jawaharlal Nehru proposed the Preamble before the drafting committee of the Constitution. The Preamble is the introductory statement that outlines the principles and objectives of the Indian Constitution. It reflects the values of justice, equality, liberty, and fraternity. Although B.R. Ambedkar played a crucial role in the drafting of the Constitution as the Chairman of the drafting committee, he did not propose the Preamble. B.N. Rao, who was a constitutional expert, also contributed to the drafting but did not propose the Preamble. Mahatma Gandhi, although an influential figure in the Indian independence movement, was not directly involved in the drafting of the Constitution.