Which of the following is classified as an island nation?

Nauru is classified as an island nation because it is a small island country located in the Pacific Ocean. As an island, it is entirely surrounded by water and is recognized as an independent sovereign state. Unlike the other options, which are located on the mainland of Europe, Nauru's entire geographic and political existence is based on its status as an island. It has its own government and is a member of international organizations, further solidifying its identity as an island nation.