Explanation

A constitutional body is one that is directly mentioned in the Constitution. A statutory body is created by an Act of Parliament, while an executive body is established through government orders without a specific law or constitutional provision.

I. The Inter-State Council is correct. It derives its authority from Article 263 of the Constitution. This Article empowers the President to establish such a council for coordination, discussion, and dispute resolution between the Centre and States. Even though it is set up by a Presidential order, its constitutional backing makes it a constitutional body.

II. The National Security Council is incorrect. It was established in 1998–99 by an executive decision of the Government of India. It functions as an advisory body on national security and strategic affairs, but it has no mention in the Constitution or any statute, placing it in the category of executive bodies.

III. Zonal Councils are incorrect. These were created under the States Reorganisation Act, 1956, making them statutory bodies. Their role is to promote inter-state cooperation and coordination, especially on issues like border disputes, economic planning, and internal security, but they do not have constitutional status.

Thus, only the Inter-State Council has a constitutional origin, making the correct answer Only one.