The correct answer is option 2: Taiwan. Taiwan is not a member country of the United Nations (UN). The UN is an international organization composed of almost all recognized independent countries in the world. Its goal is to maintain international peace and security, promote human rights, foster social and economic development, and coordinate cooperation between nations.
Option 1: Greece is a member country of the UN. It has been a member since 1945 and actively participates in the organization`s activities.
Option 3: Portugal is also a member country of the UN. It joined the organization in 1955 and has been an active participant in various UN initiatives.
Option 4: Australia is a member country of the UN. It has been a member since 1945 and contributes to various UN programs and peacekeeping missions.
Overall, the provided answer is correct, and Taiwan is the country that is not a UN member.