Solid State Test - 8

X forms an fcc lattice with Y atoms, occupying all the tetrahedral voids and Z atoms occupy half the octahedral voids.
Number of X atoms per unit cell = 4
Number of Y atoms per unit cell = Number of tetrahedral voids = 8
Number of Z atoms per unit cell = 1/2 of octahedral voids = 4/2 = 2
Hence, the formula of the solid is X₂Y₄Z.

ZnS structures contain cations in alternate tetrahedral voids.

Frenkel defect is present in those compounds which have low coordination number and large difference in the size of cations and anions. Hence, due to small size of Zn²⁺ ion and large size of S^2- ion, ZnS shows this defect.

One positive ion and one negative ion missing from their positions, leaving behind a pair of holes, give rise to Schottky defect.
So, (A) – (d)
In Frenkel defect, ion leaves its correct lattice site and occupies an interstitial site.
Thus, (B) – (c)
Presence of ion in the normally vacant interstitial sites is indicative of interstitial defect.
So, (C) – (a)
Silicon doped with phosphorus shows extrinsic conduction.

The colours observed during the flame test are due to the excitement of the electrons caused by the increased temperature. The electrons "jump" from their ground state to a higher energy level. As they return to their ground state, they emit visible light.

Diamagnetic behaviour is shown by those substances which contain fully filled orbitals i.e. there are no unpaired electrons present and this condition is fulfilled by NaCl. Diamagnetic substances are weakly repelled by an external magnetic field.

Conductivity is due to the presence of impurities and defects.