The longest border between any two countries in the world is between :

Answer: A. The longest border between any two countries is between CANADA and the USA. The Canada-United States border is approximately 8,891 km long (including the Alaska-Canada border of about 2,475 km). It is the longest international land border in the world. Distractors: (B) Chile-Argentina border is about 5,300 km long (the second longest in the Americas) but shorter than Canada-USA. (C) China-India border (LAC) is about 3,488 km long. (D) Kazakhstan-Russia border is about 7,644 km, the second longest international border in the world but still less than Canada-USA. Source: syllabus Fundamentals of Physical Geography / CIA World Factbook border statistics.