i) The crystal structure of Lithium Selenide, Li2Se, is an antifluorite structure, which has anions in the icc close-packed structure with Li cations occupying all 8 tetrahedral positions. Draw the structure and calculate the density of Li2SSe. The atomic weights are: AL=6.941g/mol and ASe=87.97g/mol. The ionic radii are rL=0.073nm and rSe=0.184nm. Assume that the Selenium atoms (valance of -2 ) do not touch other Selenium atoms but that they do touch Lithium atoms. (20 points) ii) What is the maximum radius of a cation which can be accommodated in the vacant interstice of the anion array of Li2Se ? (10 points)