Explanation:

- The Narmada River flows through a rift valley, which is characterized by steep sides and a flat valley floor. It flows westward across central India, making it notable for this unique geographical feature.

- The Periyar River is the longest river in the state of Kerala, but it does not flow through a rift valley.

- The Penganga River is a tributary of the Wardha River, and it does not have a course through a rift valley.

- The Son River flows through central India, and while it has significant historical importance, it does not run through a rift valley.