Who served as the Constitutional Adviser to the Constituent Assembly of India and guided the Drafting Committee in preparing the Constitution?

Introduction / Context:
The framing of the Constitution of India involved not only the members of the Constituent Assembly and its Drafting Committee, but also an important Constitutional Adviser who prepared initial drafts and provided detailed legal guidance. This question asks for the name of that adviser, a key but sometimes overlooked figure in the constitution making process.

Given Data / Assumptions:

• The body involved is the Constituent Assembly of India.
• We are looking for the Constitutional Adviser, not the Chairman of the Drafting Committee.
• The options list several prominent individuals active around that time.
• We assume familiarity with at least the main offices and names connected with constitution making.

Concept / Approach:
While Dr B. R. Ambedkar was the Chairman of the Drafting Committee, the role of Constitutional Adviser was played by B. N. Rau. He produced an initial draft of the Constitution and gave legal and comparative constitutional advice to the Assembly and its committees. His work shaped the early structure and many technical details, which were later debated and modified by the members. Therefore, to answer correctly, we must distinguish between the political leadership of the Drafting Committee and the advisory role of the Constitutional Adviser.

Step-by-Step Solution:
Step 1: Recall that the Chairman of the Drafting Committee was Dr B. R. Ambedkar, but the question is about the adviser, not the chairman. Step 2: Identify B. N. Rau as the person officially designated as Constitutional Adviser to the Assembly. Step 3: Confirm that other prominent names had different roles, such as presidency of the Assembly or membership of the Drafting Committee. Step 4: Choose B. N. Rau as the correct answer from the options provided.

Verification / Alternative check:
Historical records of the Constituent Assembly proceedings and official documents of the Government of India clearly mention B. N. Rau as the Constitutional Adviser. He prepared an initial draft known as the Draft Constitution of October 1947. The Drafting Committee under Ambedkar then reworked this document. Because this role is repeatedly and explicitly attributed to B. N. Rau, there is no ambiguity about the correct answer.

Why Other Options Are Wrong:
B. Shiva Rao: An important commentator and chronicler of the Constituent Assembly, but not its Constitutional Adviser. B. R. Ambedkar: Chairman of the Drafting Committee, not the Constitutional Adviser. Sachchidananda Sinha: The first temporary president of the Constituent Assembly. K. M. Munshi: A prominent member of the Drafting Committee, but not the designated adviser. Their contributions were significant but do not match the specific post referred to in the question.

Common Pitfalls:
The main confusion is between the roles of Ambedkar and B. N. Rau. Many aspirants, seeing a question about the Constitution, instinctively choose Ambedkar. To avoid this, always read whether the question refers to Drafting Committee chairmanship, presidency of the Assembly, or the advisory role. Each involved a different person and set of responsibilities in the constitution making process.

Final Answer:
B. N. Rau