Q. 24

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Answer :

(a) (i) The above defect is stoichiometric because the no. of missing cation and anion is equal. (A cation is missing from 2nd row and an anion is missing from 3rd row)


(ii) This defect is called Schottky defect. It is a vacancy defect shown by anionic substances in which cation and anion are of similar size.


An example of the compound which shows this type of defect is NaCl.


(iii) Since, the cations and anions are missing from the lattice thereby creating vacancy. Thus, density of crystal decreases.


(b)



OR


(a) In terms of band theory, conductors, semi conductors and insulators can be differentiated as follows-



(b) The electrical conductivity of semi conductors increase with rise in temperature because the energy gap between valence and conduction band in semi-conductor is very small and with rise in temperature, electrons can flow from valence band to conduction band thereby increasing conductivity.


(c) Since, Y forms hcp lattice, the no. of atoms of Y =


= 4


No. of tetrahedral voids in lattice = 2 (no. of atoms of Y)


= 2


Since, X occupy 1/3rd of tetrahedral voids, then no. of atoms of X = 8 =


Formula of compound =


= X2Y3


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