Class d fire
The type of coal that burns the most efficiently is anthracite coal.
The type that burns.
Anthracite
Yes. As a general rule the faster it burns the hotter it gets.
Burns can expose the most nerve endings. Pain from burns is pretty substantial.
Maple wood burns about as well as any other type of wood. There's no exact temperature at which it burns though, as it depends on the type of fire. For burning purposes, sugar maple is by far the best.
The very hot ones
It all depends on what level it is and how you train it. The most definite answer would Arceus, because Arceus is pretty much a god, and can be the fire type. If you cheat, and make up moves, it could even be a Vulpix! But if I were to say, it would be a Blaziken with Fire Move. (Fire Move burns, puts the opponent to sleep, and every other status and has a 20% chance of killing the opponent.)
type II
Well a fire normally needs Gas Air and Oxygen so it burns when you turn the gas on the fire will automatically shows up because you are completing the triangle to make fire which is GAS+AIR+OXYGEN=fire
The type of land that is most threatended by desertification is marginal land. Marginal land generally has poor soil and has no significant time of the year when it recieves rainfall. This makes it the first type of land that is likely to become a desert.