Explanation:

- Option 1: Lord Mountbatten

- He was the last Viceroy of British India and the first Governor-General of independent India.

- He played a role in the transition of India to independence but was not involved in the drafting of the Constitution.

- Option 2: Dr. Rajendra Prasad

- He was the President of the Constituent Assembly of India.

- While he played a significant role in the Assembly, he was not the chairman of the drafting committee.

- Option 3: Dr. B. R. Ambedkar

- He was the chairman of the drafting committee of the Indian Constitution.

- Dr. Ambedkar is often hailed as the chief architect of the Indian Constitution.

- Option 4: Pandit Jawaharlal Nehru

- He was the first Prime Minister of India.

- He was instrumental in the independence movement and governance but was not the chairman of the drafting committee.