The correct answer is option 2: Two.

To understand why, let`s look at the northeastern states of India (excluding West Bengal). The northeastern states include Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim, and Tripura.

Out of these states, two of them share their borders with three other countries. These two states are Arunachal Pradesh and Tripura.

Arunachal Pradesh shares its borders with China to the north, Bhutan to the west, and Myanmar to the east. It is the only state in India that shares its borders with three countries to the east.

Tripura, on the other hand, shares its borders with Bangladesh to the west, south, and southeast. Therefore, it also shares its borders with three countries.

The other northeastern states either share their borders with fewer countries or do not share their borders with three countries.

Therefore, the correct answer is two northeastern states (excluding West Bengal) that share their borders with three other countries.