The mountain range that separates the northern european and west siberian plains is

ANSWER:

The mountain range which separates the "Northern European" and "West Siberian plains" is the Urals or Ural Mountains.

EXPLANATION:

They divide Russia into 2 parts, i.e., Europe and Asia and acts as a natural barrier to it.  They are the oldest mountains having a span of about 300 million years ago. Mount Narodnaya is the highest peak of Ural Mountains and it runs from north to Ural river in south and finally the river flows in Caspian Sea.

Ithink the correct answer is a