Which of the following rivers marks the easternmost boundary of the Himalayas?

The Himalayan mountain system is conventionally bounded, west to east, by two great river gorges: the Indus river gorge marks its western limit, and the Brahmaputra river gorge (near the Namcha Barwa syntaxis) marks its eastern limit — this west-east span is the standard basis geography textbooks use to define the Himalayas' boundary rivers.

Applying this to the given rivers: the Brahmaputra rises in Tibet, curves around the Namcha Barwa syntaxis, and enters India through Arunachal Pradesh and Assam — exactly the eastern extremity used to define the Himalayan range's limit. It is therefore the river that marks the easternmost boundary of the Himalayas.

• Jhelum belongs to the Indus system and lies in the northwestern Himalayas — near the range's western limit, not its eastern one.

• Mahanadi is a peninsular river confined to the Chhattisgarh–Odisha region, with no course through the Himalayan mountain system.

• Godavari is also a peninsular river, rising in the Western Ghats and crossing the Deccan Plateau, again with no Himalayan course.

This matches the standard NCERT Class 9 Geography statement that ‘the Brahmaputra marks the eastern-most boundary of the Himalayas,’ confirming Brahmaputra as the answer.