S. N. Mukherjee prepared a series of background papers based on a close study of the political systems obtaining in other countries. Let's break down the answer in detail:

Who is S. N. Mukherjee?
- S. N. Mukherjee is an Indian politician and a close associate of Jawaharlal Nehru, the first Prime Minister of independent India.
- Mukherjee played a significant role in the Indian independence movement and was one of the founding members of the Indian National Congress.

What are the background papers prepared by S. N. Mukherjee?
- S. N. Mukherjee prepared a series of background papers.
- These papers were based on a close study of the political systems obtaining in other countries.

Why did S. N. Mukherjee prepare these papers?
- The papers were prepared to aid the Constituent Assembly in drafting the Indian Constitution.
- The Constituent Assembly was tasked with drafting India's first Constitution after gaining independence from British rule.

What was the significance of S. N. Mukherjee's papers?
- The papers were significant as they provided the Constituent Assembly with insights into the political systems of other countries.
- This helped the Assembly in crafting a Constitution that was suited to India's unique needs and circumstances.

In conclusion, S. N. Mukherjee prepared a series of background papers to aid the Constituent Assembly in drafting India's first Constitution. These papers were based on a close study of the political systems obtaining in other countries and were significant in providing the Assembly with insights into crafting a Constitution suited to India's unique needs and circumstances.