The correct answer is option 1: Sutlej.

The reservoir Gobind Sagar is located on the Sutlej River. A reservoir is an artificial lake created by constructing a dam on a river to store and regulate water flow. Gobind Sagar is one such reservoir that was created by the Bhakra Dam on the Sutlej River.

Option 2, Son, is incorrect. The Son River is a tributary of the Ganges River and does not have a reservoir named Gobind Sagar.

Option 3, Rihand, is also incorrect. The Rihand River is a tributary of the Son River and does not have a reservoir named Gobind Sagar.

Option 4, Narmada, is also incorrect. The Narmada River flows through the states of Madhya Pradesh, Gujarat, and Maharashtra but does not have a reservoir named Gobind Sagar.

In conclusion, the correct answer is option 1, Sutlej, as the Gobind Sagar reservoir is situated on this river.