Step 1: Understanding the Question:
The question asks us to identify which of the given options is NOT a constitutional body (constitutional machinery).
Step 2: Key Concepts and Approach:
A constitutional body is one that is explicitly created and defined by the text of the Constitution itself.
Non-constitutional bodies can be statutory (created by an Act of Parliament) or extra-constitutional/executive (created by a Cabinet resolution).
We need to verify the constitutional provisions for each option.
Step 3: Detailed Explanation:
• Attorney General for India: Created under Article 76 of the Constitution, which defines the office, qualifications, and duties of the chief legal advisor to the government. Thus, it is a constitutional body.
• Election Commission: Created under Article 324 of the Constitution, which vests the superintendence, direction, and control of elections in this body. Thus, it is a constitutional body.
• Public Service Commissions: Created under Article 315 of the Constitution (for both Union and States) to conduct examinations for appointments to services. Thus, it is a constitutional body.
• NITI Aayog: Established on January 1, 2015, via an executive cabinet resolution to replace the Planning Commission. It is an executive, non-statutory, and extra-constitutional body with no mention in the text of the Constitution.
Step 4: Final Answer:
NITI Aayog is not a constitutional machinery. Therefore, Option D is the correct answer.