What of these countries was not a member of the triple alliance?

Among the countries that formed the Triple Alliance during World War I—Germany, Austria-Hungary, and Italy—Italy was initially part of the alliance but later switched sides to join the Allies in 1915. Thus, if you are asking which country was not part of the original Triple Alliance, it could refer to any nation outside of these three, such as France, Russia, or the United Kingdom, which were part of the opposing Allied Powers.