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(e) 12-16 and 15-15 group compounds:, Refer to Basic Concepts Points 16 (c), (e); 16 (6). (d) and 14 (a), (B)., , , , , , , , , , , , , , , , , , , 1S., , uiiple Choice Questions ~~ /-"" ”)y)s(}!= 8a, , nse and write the correct option(s) in the following questions., , 1. Which of the following conditions favours the existence of a substance in the solid state?, (NCERT Exemplai, , a) High temperature (b) Low temperature, ©) High thermal energy (d) Weak cohesive forces, 2. Which of the following is not a characteristic of a crystalline solid? [NCERT Exempla, , a) Definite and characteristic heat of fusion., , 5) Isotropic nature., , (©) A regular periodically repeated pattern of arrangement of constituent particles in the entire crystal., (d) A true solid, , 3. Which of the following is true about the value of refractive index of quartz glass? [VCERT Exempl., (a) Same in all directions (b) Different in different directions, , (c) Cannot be measured (d) Always zero, , ee ed a ey, , The Solid State, , De Tl oe

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oy, , ASSETTION (4) > Curses ome emo Ty Ge TCE COT SECHEETEE,, , Assertion (A) is incorrect, but Reason (R) is correct statement., , Assertion (A) :, , Reason (RK):, , Assertion (A) :, , Reason (R) :, , Assertion (A) ;, , Reason (R) :, , Assertion (A) :, , Reason (R):, , Assertion (A) :, , Reason (R), Assertion (A), , Reason (R), , Graphite is a good conductor of electricity however diamond belongs to the category of, insulators., , Graphite is soft in nature on the other hand diamond is very hard and brittle., , The total number of atoms present in a simple cubic unit cell is one., , Simple cubic unit cell has atoms at its corners, each of which is shared between eight, adjacent unit cells., , The coordination number of square close packing in two dimensions is 6,, , In square close packing, each sphere is in contact with four of its neighbours., , Total number of octahedral voids present in unit cell of cubic close packing including, the one that is present at the body centre. is four,, , Besides the body centre there is one octahedral void present at the centre of cach of the, six faces of the unit cell and each of which is shared between two adjacent unit cells., The packing efficiency is maximum for the fcc structure., , The cordination number is 12 in fee stractures,, , Semiconductors arc solids with conductivities in the intermediate range from 107° — 10*, ohm” m™., , Intermediate conductivity in semiconductor is due to partially filled valence band,, , The Solid State 31