The correct option is Communications.
Explanation
The Seventh Schedule of the Indian Constitution, read with Article 246, distributes legislative powers between the Union and the States through three lists: the Union List (List I), the State List (List II), and the Concurrent List (List III). Subjects of national importance are generally placed in the Union List, while subjects of local or regional interest are placed in the State List.
Analysis of Options:
- Communications Communications: This subject is listed under the Union List (Entry 31). It encompasses posts and telegraphs, telephones, wireless, broadcasting, and other like forms of communication. Due to the need for a uniform national network and security implications, it is under the exclusive domain of the Parliament.
- Police Police: This is listed under the State List (Entry 2). It includes railway and village police, subject to certain provisions of the Union List.
- Irrigation Irrigation: This falls under the State List (Entry 17). The entry covers "Water, that is to say, water supplies, irrigation and canals, drainage and embankments, water storage and water power," subject to the provisions of Entry 56 of List I (Regulation and development of inter-State rivers).
- Commerce Commerce: "Trade and commerce within the State" is listed under the State List (Entry 26). However, inter-state trade and commerce fall under the Union List.
Key Takeaway: Subjects requiring a uniform national policy, such as Defense, Foreign Affairs, and Communications, are enumerated in the Union List, whereas subjects concerning local governance and order, such as Police, Public Health, and Agriculture, are in the State List.