Q. Occurrence of group 13 element?

Both boron and aluminium have a high affinity for oxygen, so neither of them is found native. Boron occurs principally in the earth's crust as boric acid, H₃B0₃ and as borates, such as, borax, Na₂B₄0₇-10H₂0, kernite, Na₂B₄0₇.4H₂0 and colemanite, Ca₂B,₆0₁₁.5H20. Aluminium is the most abundant metal (8.13%) in the earth's crust and is the third most abundant element, next only to oxygen (46.6%) and silicon (27.7%)). It occurs widely in the complex alumino-silicates, such as, clay from which, however, it cannot be extracted economically. The important ores of aluminium are bauxite, Al₂,0₃,-xH₂0, where x = 1-3, cryolite, Na₃Fl₆, and  corundum, Al₂0₃;. Gallium (1.9 x 10^-3%), indium\(2.1 x lod⁵%) and thallium (7.0  x 10⁵%)) are much less abundant than aluminium. Gallium and indium are found in aluminium and zinc ores. But even the richest sources contain less than 1% gallium and still less indium. Thallium is widely distributed in nature and occurs in sulphide ores of zinc, lead, copper and iron.