The correct answer is a) Idukki.
The Idukki Dam is a gravity dam on the Periyar River in the Idukki district of Kerala, India. It is the largest hydroelectric project in Kerala and the second largest in India. The dam was constructed between 1961 and 1974 and is operated by the Kerala State Electricity Board. The dam has a height of 168 meters (551 feet) and a length of 360 meters (1,181 feet). The reservoir created by the dam, Idukki Reservoir, has a capacity of 2,147 million cubic meters (75.2 billion cubic feet). The dam generates 2,100 megawatts of electricity.
The Sabarigiri Hydroelectric Project is a proposed hydroelectric project on the Sabari River in the Idukki district of Kerala, India. The project is being developed by the Kerala State Electricity Board. The project will have a installed capacity of 1,000 megawatts.
The Idamalayar Hydroelectric Project is a hydroelectric project on the Idamalayar River in the Idukki district of Kerala, India. The project is being developed by the Kerala State Electricity Board. The project has an installed capacity of 240 megawatts.
The Sholayar Hydroelectric Project is a hydroelectric project on the Sholayar River in the Palakkad district of Kerala, India. The project is being developed by the Kerala State Electricity Board. The project has an installed capacity of 120 megawatts.