Explanation:

About Deucha-Pachami Mines

• Deucha-Pachami-Dewanganj-Harinsinga coal block is the second-largest coal block in the world located in West Bengal’s Birbhoom district. ; it is the largest in India. 
• The block has a thick coal seam trapped between equally thick layers of rocks, mostly basalt. It has a great economic value.
• The existence of these thick basalt layers, however, makes mining of coal difficult; foreign investment and technology will be hence needed for mining. 
• An estimated 1,198 million tonnes of coal and 1,400 million tonnes of basalt are in the block.
• The block is spread over 13.7 square kilometres.

Hence option 3rd is correct.