Final answer:
The Lena River is the 11th longest river in the world, the easternmost of the three great Siberian rivers, and it flows into the Arctic Ocean with its source in the Baikal Mountains.
Step-by-step explanation:
The easternmost of the three great Siberian rivers, which is the 11th longest river in the world, and flows into the Arctic Ocean with its source in the Baikal Mountains, is the Lena River. This river is not only one of the longest river systems in the world but is also notable for flowing through the Eastern Frontier, a region marked by planned cities, industrial plants, and raw-material processing centers around the Lake Baikal region. The Lake Baikal itself is an extraordinary body of freshwater, known for holding more fresh water than all the U.S. Great Lakes combined and being the world's deepest lake.