Which hydropower plant in Bhutan was inaugurated in 2019 by Indian Prime Minister Narendra Modi?

Which of the following is the oldest hydropower station in India?

Shivasamudram Hydro Power Project is located in-

On which one of the following rivers is the Tehri Hydropower Complex located?

The Agreement of Kosi Irrigation and Hydroelectricity Plan in 1954 was signed between which two countries?

Kalpong Hydroelectric Power project is located in-