Explanation:

- Option 1: Dharwar

- The Dharwar geological formation is known for its rich deposits of metallic minerals, especially iron ore and manganese.

- It is not significant for coal resources in India.

- Option 2: Vindhyan

- The Vindhyan formation is primarily composed of sedimentary rocks.

- It is known for resources like limestone, but not for coal deposits.

- Option 3: Gondwana

- The Gondwana geological formation is the main source of coal deposits in India.

- It contains rich deposits of bituminous coal and is the most important coal-bearing geological formation in India.

- Option 4: Kadapa

- The Kadapa formation is known for its sedimentary rocks.

- It contains minerals like barytes, uranium, and limestone but is not known for coal.