Why are the valleys of Narmada and Tapi kept separate from typical east-flowing peninsular rivers?

Correct answer: They flow westward through rift valleys

The governing concept is the drainage pattern of the Peninsular Plateau and the influence of geological structure. Most large peninsular rivers flow eastward toward the Bay of Bengal, but the Narmada and Tapi are important exceptions. They occupy rift valleys and flow westward into the Arabian Sea, so option D correctly identifies both their direction and their structural setting. They do not rise in the Himalayas, do not flow from coral islands, and cannot form the Ganga Delta. Their westward courses are related to faulted or rifted troughs in the plateau region. Therefore the distinction is based on drainage direction and valley origin, not on the rivers’ size or water volume.