If the heating is done on one small area on the top, there will be convection. If the heating is restricted to a small fraction of the heating area, then within that area the heating will go deeper than anywhere else on the surface. Then unheated area will have a shallower region of high temperature. Then some convection will occur in the deeper layers, causing some motion on top.
This happens quite a bit during welding. Convection is very significant in welding, even when the heating is from the top.
1 is b 2 is a 3 is d 4 is a 5 is c
S + O = SO4. cracked also chemical reaction
