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12–16 and 13-15 group compounds:

The compounds formed by the combination of the elements of group 12 – and group -16 are called 12–16 compound.
Examples: ZnS, HgTe, etc.
The compounds formed by the combination of the elements of group – 13 and group -15 are called 13–15 compounds.
Examples: Ga As, AIP etc.

For fcc,
Edge length of unit cell a = 2√2r
= 2 x 1.414 x 0.144 nm
= 0.407 nm

Correct answer is: (A) ionic solids

NaCl is doped with 10^-3 mol % of SrCl₂
∴ In 100 part of NaCl = 10^-3 mol SrCl₂
1 part of NaCI = \(\frac { 10^{ -3 } }{ 100 }\) mol Srcl²
= 10^-5 mol Srcl₂
= 6.022 x 10²³ x 10^-5 Srcl₂
= 6.022 x 1018 Srcl₂
As each Sr²⁺ ion creates one void hence number of voids
= 6.022 x 10¹⁸

(i) In cubic unit cell, the atom present at corner is shared by eight simple cubic unit cells from which four are situated towards lower end and four are situated towards upper end. So actually only \(\frac { 1 }{ 8}\) part of each constituent particle is related to specific unit cell.
(ii) The atom present at the centre of body do not shared any part of neighbouring atom, so the whole atom is present in unit cell.

Ferromagnetic substances make better permanent magnets because . metal ions of a ferromagnetic substance are grouped into a small region called ‘domains’. Each domain behaves like a small magnet. Here the domains are arranged randomly. When the substance is placed in magnetic field then these domains are oriented in the direction of magnetic field. As a result strong magnetic field is produced. The arragement of domains persists even in the absence of magnetic field. Hence, the ferromagnetic substance becomes a permanent magnet.

The answer is (a) CSCl.

The answer is (d) Na₂O.

When a solid is heated, vacancy defect is produced in the crystal. Because on heating. some atoms or ions leave the lattice sites completely i.e., some lattice sites become vacant. As a result of this defect, the density of the substance decreases because some atoms/ ions leave the crystal completely.

(i) ZnS shows Frenkel defect.
(ii) AgBr shows both Frenkel as well as Schottky defects.