Which one of the following east flowing rivers of India has rift valley due to down warping ?

The correct answer is Option 1: Damodar.

The Damodar River, flowing through the Chota Nagpur Plateau, occupies a distinct rift valley. In the context of Indian geomorphology, while the Narmada and Tapi are west-flowing rift valley rivers, the Damodar is a prominent east-flowing river that flows through a structural trough created by down-warping (subsidence of the earth's crust) during the Gondwana period.

• Damodar: Its basin is characterized by faulted blocks where massive coal deposits are found, confirming its tectonic origin via down-warping.
• Mahanadi: It flows through a broad basin and deltaic region, lacking a true structural rift valley of this nature.
• Sone: While it follows a fault line (Son-Narmada Lineament), it is a north-flowing tributary of the Ganga.
• Yamuna: It is an antecedent Himalayan river flowing through the Indo-Gangetic plains, not a rift valley.

Thus, Damodar is the most accurate example of an east-flowing river shaped by crustal down-warping.