The closest railway station to Kohima, the capital city, is located in:

The correct answer is: a) Dimapur.

Dimapur is the nearest railway station to Kohima, the capital city of Nagaland. It is located about 80 kilometers from Kohima. The railway station is well-connected to other major cities in India, such as New Delhi, Kolkata, and Chennai.

The other options are incorrect because they are not located near Kohima. Mokokchung is located about 150 kilometers from Kohima, Wokha is located about 180 kilometers from Kohima, and Mon is located about 250 kilometers from Kohima.