Question

What are piedmont plains?? Why alluvial soil is more common in these plains?

Answer 1

Generally the word "Piedmont", refers to the foot of a mountain. So,"Piedmont plain"refers to flat areas at the feet of mountains

Answer 2

In the upper reaches of energy river valley i.e. near the place of the break of slope, the soils are coats. Such soils are more common in Piedmont plains such as Duars, Cho's and Terai.