Question

explain the reason for dense railway network in north indian plains

Answer 1

The conditions out there in the North Indian plains are very suitable for the railway transportation..
Neither are there a large number of rivers nor is the terrain out there difficult for railways to be built..
These conditions are in favour of railways out there and hence the railways network in North Indian plains are dense..
The reason is as simple as that..

Hope it helps..

Answer 2

because the land is slope