Option 2, Thermal power, has the largest share in power generation in India. Thermal power plants generate electricity by burning various fuels such as coal, natural gas, or oil to produce steam, which then drives turbines to generate electricity. These plants are generally large and widely distributed across the country, contributing to their dominant share in power generation.

While atomic power (option 1), hydro power (option 3), and wind power (option 4) also contribute significantly to India`s power generation, they do not surpass the share of thermal power. Atomic power relies on nuclear reactions, hydro power harnesses the energy of flowing water, and wind power utilizes wind turbines to generate electricity. However, in terms of overall contribution, thermal power remains the largest source in India.