The Andes mountains, the longest continental mountain range in the world, primarily pass through the western side of South America, intersecting with several countries. From the list provided, the Andes traverse Bolivia, Colombia, Ecuador, and Venezuela, making the correct count four. While Brazil and Paraguay are in proximity, they do not have the Andes mountain range running through them. This distinction is essential for understanding the geographical distribution of the Andes, which plays a significant role in the climate, ecology, and human geography of the Andes-adjacent nations as noted in NCERT geography texts and other standard reference materials used for UPSC preparation.