Explanation:
The correct answer is C: National Advisory Council.
Constitutional bodies are those that are mentioned and established in the Constitution of India. They have specific roles and functions defined by the Constitution itself. The Planning Commission and the Election Commission are both examples of constitutional bodies.
The Planning Commission was a constitutional body that was responsible for formulating five-year plans and advising the government on economic and social issues. However, the Planning Commission was replaced by the NITI Aayog in 2015, making it no longer a constitutional body.
The National Advisory Council (NAC) was not a constitutional body. It was a non-statutory body that was set up by the government to advise on various policy issues. It was dissolved in 2014.
The Inter-State Council is a constitutional body that was established to facilitate coordination between the states and the central government. It is responsible for discussing and resolving disputes between states and ensuring the smooth working of federalism in India.
In summary, the National Advisory Council (NAC) is not a constitutional body, while the Election Commission and Inter-State Council are constitutional bodies.

Planning Commission
The Planning Commission was a non-constitutional and non-statutory body in India that was responsible for formulating five-year plans for the country's development. It was established in 1950 and had the Prime Minister as its ex-officio Chairman. The Planning Commission was dissolved in 2014 and replaced by the NITI Aayog, which is a policy think tank.

Constitutional Bodies
Constitutional bodies are those that are mentioned in the Constitution of India and derive their powers and functions directly from it. These bodies are independent and autonomous in their functioning, providing checks and balances in the democratic system. Some examples of constitutional bodies in India include the Election Commission, the Union Public Service Commission, and the Comptroller and Auditor General of India.

Non-Constitutional Bodies
Non-constitutional bodies, on the other hand, are those that are not mentioned in the Constitution and do not derive their powers directly from it. These bodies are generally created by executive orders or legislation and have a specific mandate or purpose. Examples of non-constitutional bodies in India include the Planning Commission (now replaced by NITI Aayog), the National Advisory Council, and the Inter-State Council.

Conclusion
In conclusion, the Planning Commission is not a constitutional body as it was not mentioned in the Constitution and did not derive its powers directly from it. It was a non-constitutional and non-statutory body that played a crucial role in the economic planning and development of India before being replaced by the NITI Aayog.