211. The Sun's heat and light energy reaches the Earth by which one of the following modes of transmission? 212. At the core of the Earth, the estimated temperature is to be around? 213. Archipelago mean? 214. The mean radius of the Earth is approx.? 215. Of the total volume of the Earth - the three (03) layers - the crust, the mantle, and the core, constitute respectively? 216. Which one of the following layers of the Earth is believed to have the heaviest mineral materials of highest density? 217. The heaviest silicates named as "Sima" or Silica + magnesium are most abundant in the? 218. The principal reason for the formation of metamorphic rocks is? 219. Which one of the following regions of the world is most thickly populated? 220. What is the average density of population in the world in 2013?