Wood charcoal is prepared by pilling logs of wood, one above the other with a gap in the center of the pile. What substance is used to prevent the entry of air during the above process?

The correct answer is: Wet clay

The correct option is b)Wet clay.
Charcoal is made by heating wood under a limited supply of air. Local charcoal is made by stacking logs with a gap in the middle. The heap is covered with wet clay to prevent the ingress of air. A few holes remain at the bottom of the stack.