The correct answer is [d] Prem Bihari Narain

Reason :
Prem Behari Narain Raizada (Saxena) is the man who hand wrote the original Constitution of India. Raizada over his desk in the Constitution Hall (now Constitution Club) for six months to handwrite 395 articles, 8 schedules, and a preamble in both English and Hindi.

Chief Draftsman of the Constitution in the Constituent Assembly:

The correct answer is option 'B' - B.R. Ambedkar.

B.R. Ambedkar, also known as Babasaheb Ambedkar, was the chief draftsman of the Constitution of India. He played a crucial role in framing and drafting the Constitution as the Chairman of the Drafting Committee of the Constituent Assembly.

B.R. Ambedkar's Contribution:

1. Chairman of the Drafting Committee:
- B.R. Ambedkar was appointed as the Chairman of the Drafting Committee on 29th August 1947.
- The Drafting Committee was responsible for preparing the initial draft of the Constitution based on the discussions and deliberations held in the Constituent Assembly.

2. Framing the Constitution:
- Ambedkar played a pivotal role in shaping the Constitution of India.
- He was responsible for drafting the Constitution, taking inputs from various members of the Constituent Assembly.
- Ambedkar's expertise in law and his understanding of social issues helped in addressing the concerns of various sections of society while drafting the Constitution.

3. Incorporating Social Justice:
- Ambedkar was a strong advocate for social justice and equality.
- He ensured that the Constitution reflected the principles of equality, justice, and the protection of fundamental rights for all citizens.
- Ambedkar fought for the inclusion of provisions such as abolition of untouchability, protection of the rights of marginalized communities, and reservations for Scheduled Castes and Scheduled Tribes.

4. Influential Speeches:
- Ambedkar delivered several influential speeches during the debates in the Constituent Assembly.
- His speeches highlighted the importance of fundamental rights, equality before the law, and the need for social reform.
- Ambedkar's ideas and arguments had a significant impact on the framing of the Constitution.

Conclusion:

B.R. Ambedkar's role as the chief draftsman of the Constitution and Chairman of the Drafting Committee was instrumental in the framing of the Constitution of India. His commitment to social justice and his understanding of legal and constitutional principles helped in creating a comprehensive and inclusive Constitution that continues to guide the nation.