The correct answer is (a) Hydropower.
Sikkim is a mountainous state in northeastern India. It is one of the most hydropower-rich states in India, with an installed hydropower capacity of over 1,000 MW. The state’s hydropower potential is estimated to be over 3,000 MW.
The main hydropower projects in Sikkim are the Teesta Stage III Hydroelectric Project, the Teesta Stage IV Hydroelectric Project, the Rangit Hydroelectric Project, and the Rungeet Hydroelectric Project. These projects provide electricity to the state of Sikkim and to other parts of India.
Thermal power (coal) is not a major source of electricity generation in Sikkim. There is one thermal power plant in the state, but it is not operational.
Solar power and wind power are also not major sources of electricity generation in Sikkim. There are a few small solar and wind power projects in the state, but they do not contribute significantly to the state’s electricity generation.
In conclusion, the primary source of electricity generation in Sikkim is hydropower.