Which physical process formed the landform along the northeastern border of India?

Collision of Tectonic plates

Explanation:

The north-eastern side of Indian Plate is convergent with Euarasian plate. This collision of tectonic plates form a convergent plate boundary & lead to subduction. It refers to the zone destroyed & production of mountains. This collision, convergence, subduction lead to formation of Himalaya & Hindu Kush mountains in north eastern part of India