The primary source of electricity generation in Nagaland is:

Hydropower
Thermal Power
Solar Power
Nuclear Power

The primary source of electricity generation in Nagaland is hydropower. Hydropower is the use of water in its natural state or collected in reservoirs to generate electricity. It is a renewable energy source that does not produce greenhouse gases.

Thermal power is the use of heat to generate electricity. Thermal power plants burn fossil fuels such as coal, oil, or natural gas to produce heat. The heat is then used to boil water, which turns a turbine that generates electricity. Thermal power plants are the most common type of power plant in the world.

Solar power is the use of sunlight to generate electricity. Solar panels convert sunlight into electricity using photovoltaic cells. Solar power is a renewable energy source that does not produce greenhouse gases.

Nuclear power is the use of nuclear fission to generate electricity. Nuclear power plants use uranium to produce heat, which is then used to boil water, which turns a turbine that generates electricity. Nuclear power plants are a low-carbon source of electricity, but they produce radioactive waste.

The correct answer is: a) Hydropower.