Explanation:

- Option 1: 20 Gigawatt: Initially, the Government of India set a target of achieving 20 GW of solar power by 2022, but later increased it significantly.

- Option 2: 40 GW: This was not an official target set by India but could be confused with various ambitious steps being taken over the years.

- Option 3: 80 Gigawatt: India never set a target of 80 GW for solar capacity by 2022.

- Option 4: 100 Gigawatt: This is the correct and official target set by the Indian government for solar power capacity by 2022, aiming to boost renewable energy significantly.