Which one among the following statements about NATO is not correct ?

Statement 2 is incorrect because the United States is a founding member of NATO, not an 'ex officio' member. NATO was created in 1949 by the United States, Canada, and several Western European nations to provide collective security [3]. Statement 1 is correct as NATO is a collective defence organization where an attack against one member is considered an attack against all [3]. Statement 3 is correct; Turkey joined the alliance in 1952 during the first round of enlargement [3]. Regarding statement 4, NATO had exactly 28 independent member states between 2009 (after Albania and Croatia joined) and 2017 (when Montenegro joined). Since the question likely dates from that period, statement 4 was factually accurate at the time of the exam. The US has always been a full, primary member of the North Atlantic Council, the alliance's principal political decision-making body [2].

Sources

1. [3] https://en.wikipedia.org/wiki/Enlargement_of_NATO
2. [2] https://history.state.gov/milestones/1945-1952/nato