(a) An element has atomic mass $93\mathrm{g}{\mathrm{mol}}^{-1}$ and density $11.5\mathrm{g}{\mathrm{cm}}^{-3}$ If the edge length of its unit cell is 300 pm, identify the type of unit cell.
(b) Write any two differences between amorphous solids and crystalline solids.
OR
(a) Calculate the number of unit cells in $8.1\mathrm{g}$ of aluminium if it crystallizes in a f.c.c. structure. (Atomic mass of $\mathrm{Al}=27\mathrm{g}{\mathrm{mol}}^{-1}$ )
(b) Give reasons:
(i) In stoichiometric defects, $\mathrm{NaCl}$ exhibits Schottky defect and not Frenkel defect.
(ii) Silicon on doping with phosphorus forms n-type semiconductor.
(iii) Ferrimagnetic substances show better magnetism than antiferromagnetic substances.