The correct answer is
Narmada.
The Narmada river, also called the Rewa, is a river in central India.
It is also known as the "Life Line of Gujarat and Madhya Pradesh" for its huge contribution to those two states.
The Narmada and the Tapi are the two rivers of India that flow through troughs formed by faults (rift valleys) in the mountains.
The Narmada flows through the Narmada rift valley between the Vindhya and the Satpura ranges, while the Tapi flows through the Tapi rift valley.
The Son, the Godavari and the Cauveri do not flow through such fault-troughs.
Hence, the river that flows through a fault-trough is the Narmada.