The correct answer is option 2: Rajendra Prasad. Rajendra Prasad was elected as the President of the Constituent Assembly of India in 1946. He held this position until 1949 when the Constitution of India was adopted and the Constituent Assembly ceased to exist.

Option 1: B. R. Ambedkar was a member of the Constituent Assembly and played a significant role in drafting the Constitution of India as the Chairman of the Drafting Committee. However, he was not the President of the Constituent Assembly.

Option 3: Alladi Krishnaswami Aiyar, like B. R. Ambedkar, was also a member of the Constituent Assembly. He contributed to the framing of the Constitution as a lawyer and constitutional expert. However, he was not the President of the Constituent Assembly.

Option 4: Sarvepalli Radhakrishnan was a philosopher, statesman, and the first Vice President of India (1952-1962) and the second President of India (1962-1967). However, he did not hold the position of President of the Constituent Assembly.

Overall, Rajendra Prasad was the President of the Constituent Assembly of India, while the other