The correct answer is (b), Kosi.
Superimposed drainage is a type of drainage pattern that occurs when a river system erodes through a region of different rock types. The river will follow the path of least resistance, which is often the direction of the underlying rock strata. However, if the river encounters a region of harder rock, it will be forced to change course. This can result in a river system that appears to be “superimposed” on the underlying geology.
The Kosi River is a good example of a superimposed drainage system. The river originates in the Himalayas and flows eastward across the Ganges Plain. The Ganges Plain is composed of relatively soft sedimentary rocks, which the Kosi River has been able to erode easily. However, when the river reaches the Himalayas, it encounters a region of harder rock. This has forced the river to change course several times, resulting in a river system that appears to be “superimposed” on the underlying geology.
The other options are not examples of superimposed drainage. The Alaknanda River, Chambal River, and Godavari River all flow through regions of relatively soft sedimentary rocks. As a result, they have been able to erode these rocks easily and maintain a relatively straight course.