The correct answer is option 3: Nagpur. Nagpur is called the `zero-mile centre` of India because it is considered to be the geographical center of the country. This term `zero-mile centre` refers to a point from which distances to other cities or locations within the country are measured. In the case of Nagpur, it is located exactly at the center of India, and hence it serves as a reference point for calculating distances.
Option 1: Kanpur is not called the `zero-mile centre` of India. Kanpur is a city in the state of Uttar Pradesh, known for its industrial and commercial significance.
Option 2: Allahabad is also not referred to as the `zero-mile centre` of India. Allahabad, now known as Prayagraj, is a city in Uttar Pradesh and is famous for its confluence of three rivers - the Ganges, Yamuna, and Saraswati.
Option 4: New Delhi, the capital city of India, is not known as the `zero-mile centre` of India. However, it is a significant city and serves as the political and administrative center of the country.
In conclusion, Nagpur is called the `zero-mile centre` of India because it is the geographical center