Final answer:
Indonesia is the country that occupies 5/6 of the island it is on, sharing some of its islands with neighboring countries and being known as the world's largest archipelago state.
Step-by-step explanation:
The country that occupies 5/6 of the island it is on is Indonesia. Indonesia, as a vast archipelago, shares some of its main islands with other countries. Notably, the island of Borneo is divided between Indonesia, Malaysia, and Brunei; the island of Timor is split between Indonesia and East Timor; and the western portion of the island of New Guinea is shared with Papua New Guinea. Indonesia is known to be the sixteenth-largest country in the world by land area and with over 17,500 islands, it is the world's largest archipelago state. Indonesia's extensive territory encompasses a significant amount of the globe's biodiversity and cultural diversity, making it a particularly unique country both geographically and culturally.