Which Indian state shares the longest border with Nagaland?

The correct answer is: a) Assam.

Assam shares the longest border with Nagaland, with a total length of 518 kilometers. The two states are separated by the Brahmaputra River. The border between Assam and Nagaland was established in 1972, when the Nagaland state was created.

Option b) Manipur is incorrect because the border between Manipur and Nagaland is only 398 kilometers long.

Option c) Arunachal Pradesh is incorrect because the border between Arunachal Pradesh and Nagaland is only 430 kilometers long.

Option d) Meghalaya is incorrect because the border between Meghalaya and Nagaland is only 220 kilometers long.