The correct answer is option 1: Krishna. The Nagaijunasagar dam is indeed constructed on the Krishna River. Nagaijunasagar dam is one of the largest dams in India and is located in the state of Telangana. It is built across the Krishna River, which is one of the major rivers in India. The dam serves multiple purposes including irrigation, hydroelectric power generation, and flood control. It has a capacity to store a large amount of water, which is used for irrigation in the surrounding regions. The hydroelectric power generated by the dam helps in meeting the electricity requirements of the nearby areas. Overall, the Nagaijunasagar dam plays a significant role in the development and management of water resources in the Krishna River basin.