Since the thumbtack on material B dropped first, this suggests that heat from the source was conducted more quickly to the wax on material B, causing it to melt faster than the wax on A.

So we can infer that material B is a better conductor of heat than material A.


For the next set-up,

The heat that the paper gains from the source would be conducted away more quickly by Material B than by Material A.

Or in other words, Material A would conduct the heat away from the paper slower than Material B.

So, the side of the paper that is covering Material A will burn first as the heat is not conducted away fast enough i.e there is sufficient amount of heat to result in combustion.

Answer is (2)


Take note that it is the material conducting heat away from the paper, not towards it.

Notice that the materials are not fully covered by the paper, so those exposed parts will gain heat from the rest of the covered parts and the paper as well.

Thanks J for the detail explanation.