Which one of the following countries is not a UN member country?

Taiwan is not a member of the United Nations. While it was a founding member and held a permanent seat on the Security Council as the Republic of China (ROC), it was expelled in 1971 following UN General Assembly Resolution 2758 [t1][t2]. This resolution recognized the People's Republic of China (PRC) as the only legitimate representative of China to the UN [t3]. Currently, the UN considers Taiwan to be an integral part of China with no separate governmental status [t3]. In contrast, Australia is a founding member [c2][t5], and both Greece and Portugal are long-standing member states [t5]. As of 2025, there are 193 UN member states, a list that excludes Taiwan but includes the other three options [c1][t4]. Taiwan's status remains that of a non-member, as it is not recognized as an independent sovereign state by the majority of the UN membership [t2].

Sources

1. [1] https://en.wikipedia.org/wiki/Taiwan_and_the_United_Nations
2. [2] https://losangeles.china-consulate.gov.cn/eng//lghd/202405/t20240518_11306696.htm
3. [3] Contemporary World Politics, Textbook in political science for Class XII (NCERT 2025 ed.) > Chapter 4: International Organisations > Chapter 4 International Organisations > p. 50
4. [4] Contemporary World Politics, Textbook in political science for Class XII (NCERT 2025 ed.) > Chapter 4: International Organisations > Major contributors to the UN regular budget for 2019 > p. 53
5. [5] https://www.un.int/protocol/sites/www.un.int/files/Protocol%20and%20Liaison%20Service/officialnamesofcountries.pdf