In the fluorite structure, the coordination number of Ca²⁺ ion is :

Solution

In fluorite structure each F^- ion is surrounded by four Ca⁺⁺ ions whereas each Ca⁺⁺ is surrounded by eight F^- ions,giving a body centred cubic arrangement. Thus the co-ordination number of Ca⁺⁺ and F^- are 8 and 4 respectively.

For orthorhombic system axial ratios are a ≠ b ≠ c and the axial angles are

? = ? = ? ≠ 90°
? = ? = ? = 90°
? = ? = ? = 90°,? = 90°
? ≠ ? ≠ ? = 90°

Solution

For orthorhombic system ? = ? = ? = 90°

In stoichiometric defects, the types of compound exhibit Frenkel defects have/has

Low co-ordination nos.
High co-ordination
Small difference in the size of cations and anions
None of these

Solution

In stoichiometric Frenkel defects occurs in those compound which have
(i)Low C.N.
(ii)Large difference in size of cations and anions

Edge length of a cube is 400 pm, its body diagonal would be

566 pm
600 pm
500 pm
693 pm

Solution

In NaCl crystal each Cl–ion is surrounded by

4 Na⁺ ions
6 Na⁺ ions
1 Na⁺ ions
2 Na⁺ ions

Solution

The radius ratio in CsCl is 0.93. The expected lattice structure is

tetrahedral
square planar
octahedral
body-centred cubic

Solution

Since the radius ratio of CsCl is 0.93, it is expected to have a body centred cubic structure.

A solid is made of two elements X and Z. The atoms Z are in ccp arrangement while the atoms X occupy all the tetrahedral sites. What is the formula of the compound?

XZ
XZ₂
X₂Z
X₂Z₃

Solution

Let the number of Z atoms in the ccp arrangement= 100
Thus the number of tetrahedral sites = 200
Since all the tetrahedral sites are occupied by X atoms,the number of X atoms = 200
Hence ratio of X: Z= 2 : 1
Thus the formula is X₂Z.

A solid has a structure in which ‘W’ atoms are located at the corners of a cubic lattice ‘O’ atoms at the centre of edges and Na atoms at the centre of the cube. The formula for the compound is

Na₂WO₃
Na₂WO₂
NaWO₂
NaWO₃

Solution

In a unit cell, W atoms at the corner = \(\frac{1}{8}\) × 8 = 1
O-atoms at the centre of edges = \(\frac{1}{4}\) × 12 = 3
Na-atoms at the centre of the cube = 1
W : O : Na = 1: 3 : 1
Hence, formula = NaWO₃

The element which is used as semiconductor is

Solution

Semiconductors are those solids which are good conductors of electricity at room temperature but behave as insulators at room temperature, e.g., silicon and germanium.

The ionic radii of X⁺ and Y^– ions are 146 and 216 pm respectively. The probable type of structure shown by it is

CsCl type
Rock salt type
Zinc blend type
CaF₂ type

Solution

The radius ratio = \(\frac{r^{+}}{r^{-}} = \frac{146}{216}\) = 0.675.
It lies between 0.414– 0.732. Hence, it exhibits rock salt type structure.

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