Which of the following is not a constitutional body?

NITI Aayog is not a constitutional body; it's an apex public policy think tank of the Government of India, established through an executive resolution, not the Constitution.  The office of the Comptroller and Auditor General (CAG) is a constitutional body in India, as it is mentioned in Article 148 of the Constitution.  These bodies are established and derive their powers directly from the Constitution of India.  Finance Commission: Established under Article 280 of the Constitution to advise on matters related to distribution of tax revenues between the Union and the States.  Union Public Service Commission (UPSC): Established under Article 315 of the Constitution to conduct civil services examinations and other related functions.  Election Commission: Established under Article 324 of the Constitution to conduct free and fair elections.