The correct answer is option 1, coal mining.

Coal mining is the most labour-intensive mining activity compared to the other options listed. Labour-intensive refers to the amount of human labor required in the mining process. Coal mining involves various manual tasks such as drilling, digging, and extracting coal from the ground. These tasks require a significant amount of physical labor.

On the other hand, the mining of manganese, iron ore, and copper may involve the use of heavy machinery and equipment, reducing the reliance on manual labor. Although some manual tasks may still be involved in these mining activities, they do not require as much labor as coal mining.

Coal mining also often involves working in underground mines, which adds to the complexity and physical demands of the job. The extraction process for coal can be more challenging compared to other minerals, requiring more effort and manpower.

In summary, coal mining is more labor-intensive compared to the mining of manganese, iron ore, and copper due to the manual tasks involved and the nature of the mining environment.