Who among the following eminent jurists served as the Constitutional Adviser to the Constituent Assembly of India during the framing of the Constitution?

Introduction / Context:
The Constitution of India was drafted by the Constituent Assembly with the help of many experts and leaders. While Dr. B. R. Ambedkar is widely known as the Chairman of the Drafting Committee, there was also a Constitutional Adviser who played a crucial role in preparing initial drafts and offering legal guidance. This question asks you to identify that adviser.

Given Data / Assumptions:
- The question is about the Constitutional Adviser to the Constituent Assembly, not the Chairman of the Drafting Committee.
- Four names are provided, all associated with public life, law or the Constituent Assembly in some way.
- Only one of these individuals officially served as Constitutional Adviser.

Concept / Approach:
B. N. Rau (Benegal Narsing Rau) was an eminent civil servant and jurist who served as the Constitutional Adviser to the Constituent Assembly. He helped in preparing the initial draft of the Constitution, examined foreign constitutions and provided expert legal advice. His work laid the foundation for the detailed draft later prepared and refined by the Drafting Committee under Dr. B. R. Ambedkar.

Step-by-Step Solution:
Step 1: Distinguish between the Constitutional Adviser and the Chairman of the Drafting Committee. Dr. B. R. Ambedkar was Chairman, not Adviser. Step 2: Recall that B. N. Rau, a senior civil servant and jurist, was appointed as Constitutional Adviser. Step 3: V. N. Menon was a close associate in the process but is better known for his role as secretary and in the transfer of power context. Step 4: Sachidanand Sinha served as the first temporary President of the Constituent Assembly, not as Constitutional Adviser. Step 5: H. N. Kunzru was a prominent member of the Assembly but not the Adviser. Therefore, B. N. Rau is the correct answer.

Verification / Alternative check:
Standard Indian polity books and historical accounts of the making of the Constitution mention B. N. Rau as the Constitutional Adviser. They describe how he studied other constitutions and prepared memoranda and drafts which guided the later work of the Drafting Committee.

Why Other Options Are Wrong:
- V. N. Menon: Known for his role in administrative and political negotiations, not officially as Constitutional Adviser.
- Sachidanand Sinha: First temporary President of the Constituent Assembly, not its Adviser.
- H. N. Kunzru: A respected member of the Assembly but not the person who held the adviser position.

Common Pitfalls:
A common mistake is to confuse the Constitutional Adviser with either the President of the Assembly or the Chairman of the Drafting Committee. Because multiple leading figures worked together, names can easily be mixed up. To avoid this, remember that B. N. Rau is specifically associated with the advisory and drafting preparation role.

Final Answer:
The Constitutional Adviser to the Constituent Assembly of India was B. N. Rau.