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. and guctile?, , jleable, 9. What type of solids are electrical conductor ma, , Ans: Metallic solids ,, 10. Give the significance of @ lattice point ad parti n crystal abe =, Ans: A lattice point is the position occupied by the ae tically 18 called crystal ,, representation of the lattice points in a crys agramma, 11. Name the parameters that characterise a unit cell., Ans: (i) The length of the edges or edge lengths a, b and ¢, (ii) The angles between the pair of edges; Pandy, 12. Distinguish between, (i) Hexagonal and monoclinic unit cells, (ii) Face-centred and end-centred unit cells, Ans: (i) For hexagonal unit cell, a = beca=f, For monoclinic unit cell, a # b #6, a=7= 90", B#90°, (ii) A unit cell containing one constituent particle at the centre 0!, particles at the comers 1s called a face centred unit cell., End-Centred unit cells contain one constituent particle each at the centres of two opposite, faces in addition to the particles at the comers., 13. Explain how much portion of an atom located at (i) corner and (ii) body centre of a cubic unit, cell is part of its neighbouring unit cell., Ans: (i) ‘Anatom at the corner is shared by eight other unit cells in three dimensional arrangement., Hence contribution of each atom at the comer is Ye,, , (ii) ‘An stom present at the body centre is not shared by any other unit cell. lt completely, , =90°,7= 120°, , feach face in addition to the