Railway network is now extensively being built in mountainous areas. Select…

Constructing a railway line in mountainous or hilly terrain is inherently difficult: steep gradients, unstable slopes, and rocky or landslide-prone ground make large-scale rail expansion possible only when engineering capability keeps pace with the terrain's demands.

India has been extending railway lines into mountainous regions such as Jammu & Kashmir, Himachal Pradesh, and the North-East precisely because modern technology now makes this feasible — tunnel-boring machines, advanced bridge and viaduct design, and slope-stabilization techniques let engineers cut through rock, span deep valleys, and control landslide risk in ways that were not possible earlier.

• It is easy to construct railways in mountains — false; mountainous terrain is difficult to build on, not easy, given steep gradients and unstable rock.

• Mountains are highly eroded — erosion refers to the transport and removal of rock and soil by natural agents (water, wind, gravity); it is a distinct geomorphic process from railway construction and does not by itself explain why more rail lines are now being built in mountainous regions.

• Mountain people are making railways — railway lines are built by government agencies and engineering contractors using specialized technology, not by the local population.

• Advanced technological developments (tunnel-boring, bridge engineering, slope stabilization) are the actual factor that makes it feasible to extend railway lines into difficult mountainous terrain.

Hence, the most suitable reason for the extensive railway construction now seen in mountainous areas is the availability of advanced technology that overcomes the terrain's natural challenges.