Option 1: Godavari- Godavari is the second longest river in India, but it does not flow through a rift valley.
Option 2: Narmada- Narmada is the correct answer. It is the only river among the given options that flows through a rift valley. The Narmada river flows through the Narmada Valley, which is a rift valley located in central India.
Option 3: Krishna- The Krishna river is one of the longest rivers in India, but it does not flow through a rift valley.
Option 4: Mahanadi- The Mahanadi river is a major river in India, but it does not flow through a rift valley.
In conclusion, the correct answer is option 2, Narmada river, as it flows through a rift valley known as the Narmada Valley.