b) What are the formulae of the following compounds consisting of linked octahedral and tetrahedral units. In each case you must draw the structure and explain how you determined the formula. (i) A discrete unit comprised of 4 vertex-linked tetrahedra. [2 marks] (ii) An infinite 2D layer comprised of edge-linked octahedra [2 marks] (iii) A discrete unit comprised of 2 face-linked octahedra [2 marks] c) Heating copper and zinc in equal molar quantities at high temperature forrms the alloy, brass. Given the atomic radius for Cu is 1.40 and Zn is 1.39 , determine the radius ratio and hence predict and draw a structure for brass. Explain clearly how you came to this conclusion and the structure drawn. [4 marks]