Which one among the following rivers is the longest ?

Among the rivers listed, the Amazon is the longest. It is widely recognized as either the longest or second-longest river in the world, with measurements ranging from approximately 6,400 km to 6,992 km [t4][t6]. It is also the world's largest river by water discharge [c1][t5]. In comparison, the Amur River (including the Argun) measures approximately 4,444 km [t3]. The Congo River (also known as the Zaire) is the deepest river and has a length of roughly 4,700 km, though it is often ranked 9th globally [t6]. The Volga, the longest river in Europe, is significantly shorter at approximately 3,530 km. Therefore, the Amazon is the longest of the four options provided. While debates exist regarding whether the Nile or Amazon is the absolute longest on Earth, the Amazon far exceeds the lengths of the Amur, Congo, and Volga [t1][t2].

Sources

1. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 5: Landforms made by Running Water > The Human Aspects of Rivers > p. 55
2. [2] https://en.wikipedia.org/wiki/List_of_rivers_by_discharge