Explanation:

• The ongoing cooperation between India and Bhutan in the hydro-power sector is covered under the 2006 bilateral agreement for cooperation and its Protocol signed in 2009. Four hydro-electric projects (HEPs) totaling 2136 MW are already operational in Bhutan and are supplying electricity to India.
• India and Bhutan have recently signed a concession agreement on the 600 MW Kholongchhu Hydroelectric Project (KHEL). The joint venture partners of the project are India’s Satluj Jal Vidyut Nigam Limited (SJVNL) and Bhutan’s Druk Green Power Corporation Limited (DGPC).
• Pancheshwar Multipurpose Project is proposed on river Mahakali known as Sarda which forms international boundary between India and Nepal.
• The 720 MW Mangdechhu was commissioned in August 2019. Two HEPs namely, 1200 MW Punatsangchhu-I, 1020 MW Punatsangchhu-II in Inter-Governmental mode and Kholongchhu HEP (600 MWs) under the joint venture mode are under various stages of implementation.

Hence option 3rd is correct.