Which one of the following pairs is not correctly matched?

Option 4 is not correctly matched. Key (Kye) Monastery — often spelled “Key Gompa” — is located in the Spiti Valley of Himachal Pradesh, not Arunachal Pradesh; it is an ancient hilltop monastery in Spiti Valley, Himachal Pradesh. Dhankar Monastery is likewise situated in Himachal Pradesh (Spiti) [1]. Rumtek Monastery is the principal seat of the Karmapa near Gangtok in Sikkim, so that pairing is correct. Tabo Monastery is also in Tabo, Spiti Valley, Himachal Pradesh, and is one of the oldest surviving Buddhist monasteries in India. Therefore the only incorrect match is Kye Monastery: Arunachal Pradesh.

Sources

1. [1] https://en.wikipedia.org/wiki/Dhankar_Gompa