The correct answer is option 3: Nagpur. Nagpur is also known as the `zero-mile centre` of India because it is geographically located at the exact center of the country. This means that Nagpur is equidistant from the southernmost point in India (Kanyakumari) and the northernmost point (Srinagar). The concept of the `zero-mile` originated during the British colonial era as a reference point to measure distances to various places across the country. Nagpur being located at this central point holds significance in terms of transportation and communication in India. It serves as a major transportation hub and plays a pivotal role in connecting various regions of the country.