INORGANIC CHEMISTRY PART-12 EXERCISE

[A. K. MACHIWAL, KENDRIYA VIDYALAYA, 7891632633]

1/11/2015

[A. K. MACHIWAL, KENDRIYA VIDYALAYA, 7891632633] Page 1

 C. ONE WORD/SENTENCE QUESTIONS (CLO 1-13)
1. Give two examples of amorphous solids.
2. Write one property of crystalline solids.
3. What type of solids are electrical conductors, malleable and ductile?
4. Name the allotrope of Carbon which exhibits superconductivity.
5. How many octahedral and tetrahedral voids are present in ccp unit cell?
6. Why common salt is sometimes yellow instead of being pure white?
7. What is the relation of edge length and radius of the atom in a face centred unit cell?
8. How the edge length is related to the radius of the sphere (atomic radius) in a body centred
unit cell?
9. What is the percentage of free space in a simple cubic unit cell?
10. Sodium metal crystallises in body centred cubic lattice with the cell edge, 4.29 Ȧ . What is
the radius of sodium atom?
11. Which point defect may lower the density of an ionic crystal?
12. What is meant by point defect in crystal?
13. What type of stoichiometric defect is shown by: (i) ZnS (ii) AgBr
14. What is unit cell?
15. Name a salt which is added to AgCl so as to produce cation vacancies.
16. Why Frenkel defects not found in pure Alkali metal halide.
17. What is the use of amorphous silica?
18. **What is the co-ordination no. of cation in Antifluorite structure?
19. **What is the Coordination Number of cation and anion in Caesium Chloride.
20. What makes Alkali metal halides sometimes coloured, which are otherwise colourless?
21. How does amorphous silica differ from quartz?
22. What is anisotropy?
D. SHORT ANSWER QUESTIONS (SA)
1. Some glass objects from ancient civilizations are found to become milky in appearance,
why?
2. Glass panes fixed to windows or doors of old buildings are found to be thicker at bottom
than at the top. Why?
3. Give the coordination number of tetrahedral and octahedral voids.
4. An element exists as hexagonal close packed structures as well as cubic close packed
structure. In which case the element would have higher density?
5. Explain how electrical neutrality is maintained in compounds showing Frenkel and
Schottky defect.
6. An element with molar mass 2.7×10-2 kg mol-1 forms a cubic unit cell with edge length 405
pm. If its density is 2.7×103 kgm-3, what is the nature of the cubic unit cell?
7. Explain how vacancies are introduced in an ionic solid when a cation of higher valence is
added as an impurity in it.
8. Ionic solids, which have anionic vacancies due to metal excess defect, develop colour.
Explain with the help of a suitable example.
9. A group 14 element is to be converted into n-type semiconductor by doping it with a
suitable impurity. To which group should this impurity belong?
10. What happens when:- (i) CsCl crystal is heated (ii)Pressure is applied on NaCl crystal.

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11. Zinc oxide is white but it turns yellow on heating. Explain.
(E) NCERT (THEORITICAL)
1. Define the term 'amorphous'. Give a few examples of amorphous solids.
2. What makes a glass different from a solid such as quartz? Under what conditions could
quartz be converted into glass?
3. Classify each of the following solids as ionic, metallic, molecular, network (covalent) or
amorphous.
(i) Tetra phosphorus decoxide (P4O10) (vii) Graphite (ii) Ammonium phosphate (NH4)3PO4
(viii) Brass (iii) SiC (ix) Rb (iv) I2 (x) LiBr (v) P4 (xi) Si (vi) Plastic
4. (i) What is meant by the term 'coordination number'? (ii) What is the coordination number
of atoms: (a) in a cubic close-packed structure? (b) in a body-centred cubic structure?
5. How can you determine the atomic mass of an unknown metal if you know its density and
the dimension of its unit cell? Explain.
6. 'Stability of a crystal is reflected in the magnitude of its melting points'. Comment. Collect
melting points of solid water, ethyl alcohol, diethyl ether and methane from a data book.
What can you say about the intermolecular forces between these molecules?
7. How will you distinguish between the following pairs of terms:
(i) Hexagonal close-packing and cubic close-packing? (ii) Crystal lattice and unit cell?
(iii) Tetrahedral void and octahedral void?
8. How many lattice points are there in one unit cell of each of the following lattice?
(i) Face-centred cubic (ii) Face-centred tetragonal (iii) Body-centred (iv) simple cubic
9. Explain (i) The basis of similarities and differences between metallic and ionic crystals.
(ii) Ionic solids are hard and brittle.
10. Calculate the efficiency of packing in case of a metal crystal for
(i) Simple cubic (ii) body-centred cubic (iii) face-centred cubic
11. A cubic solid is made of two elements P and Q. Atoms of Q are at the corners of the cube and
P at the body-centre. What is the formula of the compound? What are the coordination
numbers of P and Q?
12. If the radius of the octahedral void is r and radius of the atoms in closepacking is R, derive
relation between r and R.
13. Analysis shows that nickel oxide has the formula NiO.98O1.00. What fractions of nickel exist as
Ni2+ and Ni3+ ions?
14. What is a semiconductor? Describe the two main types of semiconductors and contrast
their conduction mechanism.
15. Non-stoichiometric cuprous oxide, Cu2O can be prepared in laboratory. In this oxide,
copper to oxygen ratio is slightly less than 2:1. Can you account for the fact that this
substance is a p-type semiconductor?
16. Ferric oxide crystallises in a hexagonal close-packed array of oxide ions with two out of
every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.
17. Classify each of the following as being either a p-type or a n-type semiconductor:
(i) Ge doped with In (ii) B doped with Si.
18. In terms of band theory, what is the difference
(i) between a conductor and an insulator (ii) between a conductor and a semiconductor?
19. Explain the following terms with suitable examples:
(i) Schottky defect (ii) Frenkel defect (iii) Interstitials and (iv) F-centres.

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20. Explain the following with suitable examples: (i) Ferromagnetism (ii) Paramagnetism
(iii) Ferrimagnetism (iv) Anti ferromagnetism (v) 12-16 and 13-15 group compounds.
NCERT (THEORITICAL-INTEXT)
21. Why are solids rigid?
22. Why do solids have a definite volume?
23. Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene,
benzoic acid, Teflon, potassium nitrate, cellophane, polyvinylchloride, fibre glass, copper.
24. Why is glass considered a super cooled liquid?
25. Refractive index of a solid is observed to have the same value along all directions. Comment
on the nature of this solid. Would it show cleavage property?
26. Classify the following solids in different categories based on the nature of intermolecular
forces operating in them:
Potassium sulphate, tin, benzene, urea, ammonia, water, zinc sulphide, graphite, rubidium,
argon, silicon carbide.
27. Solid A is a very hard electrical insulator in solid as well as in molten state and melts at
extremely high temperature. What type of solid is it?
28. Ionic solids conduct electricity in molten state but not in solid state. Explain.
29. Give the significance of a ‘lattice point’.
30. Name the parameters that characterise a unit cell.
31. Distinguish between (i) Hexagonal and monoclinic unit cells (ii) Face-centred and end-
centred unit cells.
32. Explain how much portion of an atom located at (i) corner and (ii) body centre of a cubic
unit cell is part of its neighboring unit cell.
33. A compound is formed by two elements X and Y. Atoms of the element Y (as anions) make
ccp and those of the element X (as cations) occupy all the octahedral voids. What is the
formula of the compound?
34. Atoms of element B form hcp lattice and those of the element A occupy 2/3rd of tetrahedral
voids. What is the formula of the compound formed by the elements A and B?
35. A compound is formed by two elements M and N. The element N forms ccp and atoms of M
occupy 1/3rd of tetrahedral voids. What is the formula of the compound?
36. A solid has a cubic structure in which ‘x’ atoms are located at the corners of the cube ‘y’
atoms are at the cube centres and ‘o’ atoms are at the edge centres. What is the formula of
the compound?
37. Two elements P and Q have B.C.C. and F.C.C. structures. What will be the number of
tetrahedral and octahedral voids per unit cell?
38. In a compound, oxide ions have CCP arrangement. Cations A are present in one eighth of
the tetrahedral voids and cations B occupy half the octahedral voids. What is the simplest
formula of the compound?
39. In a crystalline solid, the atoms A and B are arranged as follows:-
(a) Atoms A are arranged in ccp array. (b) Atoms B occupy all the octahedral voids and half
of the tetrahedral voids. What is the formula of the compound?
40. In compound atoms of element Y forms ccp lattice and those of element X occupy 2/3rd of
tetrahedral voids. What is the formula of the compound?
41. A cubic solid is made of two elements X and Y. Atom Y are at the corners of the cube and X
at the body centers. What is the formula of the compound?

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42. A substance AxBy crystallizes in a face centered cubic (fcc) lattice in which atoms ‘A’ occupy
each corner of the cube and atoms B occupy the centers of each face of the cube. Identify
the correct composition of the substance AxBy
43. Three elements P,Q and R crystallize in a cubic lattice with P atoms at the corners, Q atoms
at the cube centre& R atoms at the centre of the faces of the cube then what would be the
formula of the compound.
44. A compound forms hexagonal close-packed structure. What is the total number of voids in
0.5 mol of it? How many of these are tetrahedral voids.
45. What type of defect can arise when a solid is heated? Which physical property is affected by
it and in what way?
46. Calculate the concentration of cation vacancies if KCl is doped with 10-3 mole of CaCl2
47. What type of substances would make better permanent magnets, ferromagnetic or
ferrimagnetic? Justify your answer.
48. What happens when Fe3O4 is heated to 850 K temperature?
49. Calculate the number of atoms in a cubic unit cell having one atom on each corner and two
atoms on each body diagonal.
50. CaCl2 will introduce Schottky defect if added to AgCl crystal. Explain
51. Gold crystallizes in an FCC unit cell. What is the length of a side of the cell (r=0.144 nm)
52. The electrical conductivity of a metal decreases with rise in temperature while that of a
semi-conductor increases. Explain.
53. Analysis shows that a metal oxide has the empirical formula M0.98 O. Calculate the
percentage of M2+ and M3+ ions in the crystal.
(F) NCERT (NUMERICAL)
1. Silver crystallises in fcc lattice. If edge length of the cell is 4.07 × 10–8 cm and density is 10.5
g cm–3, calculate the atomic mass of silver.
2. Niobium crystallises in body-centred cubic structure. If density is 8.55 g cm–3, calculate
atomic radius of niobium using its atomic mass 92.91 u.
3. Copper Crystallizes into FCC lattice with edge length 3.61 X 10-8 cm. Show that calculated
density is in agreement with measured value of 8.92 g/cc.
4. Gold (atomic radius = 0.144 nm) crystallises in a face-centred unit cell. What is the length
of a side of the cell?
5. Aluminium crystallises in a cubic close-packed structure. Its metallic radius is 125 pm.
(i) What is the length of the side of the unit cell?
(ii) How many unit cells are there in 1.00 cm3 of aluminium?
6. If NaCl is doped with 10–3 mol % of SrCl2, what is the concentration of cation vacancies?
OTHERS (NUMERICAL)
7. If the radius of bromide ion is 0.182 pm, how large a cation can fit in each of the tetrahedral
void?
8. Iron has body centred cubic structure. The edge length of the unit cell is found to be 286
pm. What is the radius of an iron atom?
9. Calculate the density of silver which crystallizes in the F.C.C. structure. The distance
between the nearest silver atoms is 287 pm. (Molar mass of silver = 107.87 g/mole).
10. Potassium crystallizes in a body centred cubic lattice. What is the approximate number of
unit cells in 11.7 g of potassium? [ Atomic Mass of k = 39 U ]
11. The density of chromium metal is 7.2 g/cc. If the unit cell is cubic with an edge length of
289 pm, determine the type of the unit cell present in its crystals.

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 [Atomic mass of Cr = 52 U; NA = 6.02 x 1023]
12. Sodium metal crystallites in bcc lattice with the cell edge 4.29 A” .what is the radius of
sodium atom ?
13. Determine the density of BCC iron, which has a lattice parameter of 0.2866 nm.
14. An element exists in bcc structure with a cell edge of 288 pm. Density of the element is 7.2 g
cm–3 what is the atomic mass of the element?
15. Aluminum has the face-centered cubic structure with a unit cell dimension of 4.041Å. What
is density of aluminum?
16. A metal of atomic mass = 75 form a cubic lattice of edge length 5x10-8cm and density 2 g
cm-3. Calculate the radius of the atom. Given Avogadro’s number, NA = 6 x 1023.
17. Bromide ions form cubic close packed structure. Radius of Br– is 195 pm. What would be
the minimum radius of cation which fits in the tetrahedral void?
18. The edge length of the unit cell of KCl (NaCl like structure, fcc) is 6.28A°. Assuming anion
cation contact along the cell edge, calculate the radius of the potassium ion.
19. Calculate the concentration of cation vacancies if KCl is doped with 10-3 mole of CaCl2.
20. Silver forms ccp lattice and X-ray studies of its crystals show that the edge length of its unit
cell is 408.6 pm. Calculate the density of silver (Atomic mass = 107.9 u).
21. An element has a body-centred cubic (bcc) structure with a cell edge of 288 pm. The
density of the element is 7.2 g/cm3. How many atoms are present in 208 g of the element?
22. X-ray diffraction studies show that copper crystallises in an fcc unit cell with cell edge of
3.608×10-8 cm. In a separate experiment, copper is determined to have a density of 8.92
g/cm3, calculate the atomic mass of copper.
23. The unit cell of an element of atomic mass 50 u has edge length 290pm. Calculate its
density the element has bcc structure (NA = 6.022 X 1023 atoms mol-1).
24. Calculate the density of silver which crystallizes in face centered cubic form. The distance
between nearest metal atoms is 287pm (Ag= 107.87g mol-1, NA= 6.022 X 1023).
25. What is the distance between Na+ and Cl- ions in NaCl crystal if its density 2.165 g cm-3. NaCl
crystallizes in FCC lattice.
26. Find the type of lattice for cube having edge length of 400pm, atomic mass = 60 and density
=6.25 g/cc.
27. In a face centered cubic lattice Edge length of lattice cell is 2A0. The density of metal is 2.4 g
cm-3. How many units cell are present in 200g of metal.
28. A metal crystallizes as face centered cubic lattice with edge length of 450pm. Molar mass of
metal is 50g mol-1. Calculate the density of metal.
29. The edge length of the unit cell of metal having molecular mass 75 g/mol is 1 A0 which
crystallizes into cubic lattice. If the density is 2g/cm3 then find the radius of metal atom.
30. The compound CuCl has Fcc structure like ZnS, its density is 3.4 g cm-3. What is the length
of the edge of unit cell?
31. An element crystallizes in FCC structure; 200 g of this element has 4.12 X 1024 atoms. If the
density of A is 7.2 g cm-3, calculate the edge length of unit cell.

(C) One word/ one sentence (CLO)

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 (1)Plastics and Glass (2)any one property (3)metallic solids. (4) Fullerene (C60) (5)4 and 8
(6) Due to the presence of electrons in some lattice sites in place of anions these sites act as
F-centers. These electrons when excited impart color to the crystal.
4
(7)a=2 √ 2 . r (8)=a= . r (9)47.6%(10)1.86 A0(11)Schottky defect (12)The defects formed
√3
when the atoms or ions are missed or misplaced in the crystal, is called point defects. (13)
(i) Frenkel (ii) Frenkel and Schottky both(15) CdCl2
(16)Due to larger size of Alkali metal ions. (17)It is used in Photovoltaic cells(18) 4(19)8 &8
(20) It is due to F-Center (21)In amorphous silica, SiO4 tetrahedral are randomly joined to
each other whereas in quartz they are linked in a regular manner.

(D) SHORT ANSWER QUESTIONS (CLO)

1. At some temperature they undergo crystallization, which make them milky in appearance.
2. Glass is an amorphous solid, which has property of fluidity.
(E) NCERT (THEORITICAL)
(4)(i) number of nearest neighbours atoms or ions. (ii) (a) 12 (b) 8
(8) (a) 14 (b) (c) 9 (d) 8
(21)Particles in solids are closely packed, having strong force of attraction among them.
Therefore, they are incompressible and rigid.
(22) The particles in solids have strong intermolecular attraction and they are strongly held
together at fixed position, thus solids have definite volume.
(24) b/c glass has a tendency to flow, though very, slow.
(25) The solid is isotropic type i.e. amorphous solid b/c it has the same value of refrective index
along all direction. It would not show cleavage property b/c it undergoes irregular cut
(26)
Ionic solids Metallic solids Molecular solids Covalent solids
Potassium sulphate, Tin, Rubidium Benzene, Urea, Graphite, Silicon
Zinc sulphide Ammonia, Water, Argon. carbide.
(27) It is covalent solid b/c it is very hard, electrical insulator in solid as well as molten state
having higher melting point.
(28) In the crystal lattice of ionic solid, ions occupy fixed positions thus cannot move from
their position on passing electricity in ionic solids. In molten state this orderly arrangement
gets destroyed, thus ions become free to move under the influence of applied current and
hence conduct electricity in molten state.
(29) Positions of the constituent atom, molecules or ions in a crystal lattice are represented
by lattice point.
(30)A unit cell is characterized by :
i. The dimensions of unit along the three edges represented as a, b and c which may or may
not be mutually perpendicular.
ii. There are three angles in unit cell, α (between b & c), β (between a & c) & γ (between a &
b)
(31) (i) Hexagonal unit cell has only two equal edges i.e., a = b ≠ c while in monoclinic cell all
the three edges are equal i.e., a = b = c. in hexagonal unit cell α = β = 900& γ = 1200 while in
monoclinic unit cell α = γ = 900 and β ≠ 1200
(ii) Face centred unit cell contains particles at all the corners of unit cell as well as one
particle at the centre of each face. Thus it contains 4 particles per unit cell.

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 End centred unit cell contains particles at all the corners of unit cell as well as at the centre
of any two opposite faces. Thus it contains 2 particles per unit cell.
(32) (i) 1/8th part of an atom located at corner.
(ii) the whole atom, present at the centre of the body belongs to the unit cell in which it
is present. No part of it is present in neighbouring unit cell.
(33) The ccp lattice is formed by the element Y. The number of octahedral voids generated
would be equal to the number of atoms of Y present in it. Since all the octahedral voids are
occupied by the atoms of X, their number would also be equal to that of the element Y.
Thus, the atoms of elements X and Y are present in equal numbers or 1:1 ratio. Therefore,
the formula of the compound is XY.
(34) The number of tetrahedral voids formed is equal to twice the number of atoms of
element B and only 2/3rd of these are occupied by the atoms of element A. Hence the ratio
of the number of atoms of A and B is 2× (2/3):1 or 4:3 and the formula of the compound is
A4B3.
(35) The number of tetrahedral voids formed is equal to twice the number of atoms of
element N and only 1/3rd of these are occupied by the atoms of element M. Hence the ratio
of the number of atoms of M and N is 2× (1/3) :1 or 2:3 and the formula of the compound is
M2N3.
(39) AB2 (40) X4 Y3
1 1
(42)No. of ‘A’ atoms = 8 x = 1&No. of ‘B’ atoms =6 x = 3, Hence formula is AB3
8 2
1 1
(43) No. of ‘P’ atoms = 8 x = 1, No. of ‘Q’ atoms = 1&No. of ‘R’ atoms = 6 x =3
8 2
Hence the formula of compound is PQR3
(44) since we know that, the numbers of atoms in 0.5 mole = 3.01 x 1023
Then the numbers of total voids = 3N = 3 x 3.01 x 1023 = 9.03 x 1023
And the numbers of tetrahedral voids = 2N = 2 x 3.01 x 1023 = 6.02 x 1023
(45) On heating of a solid, a non-stoichiometric defect can arise. Because of such defects
crystals of solid become coloured and their electrical conductivity is affected.
 For examples: When crystals of NaCl are heated in an atmosphere of sodium vapour, the
sodium atoms are deposited on the surface of the crystal. The Cl– ions diffuse to the surface
of the crystal and combine with Na atoms to give NaCl. This happens by loss of electron by
sodium atoms to form Na+ ions. Thereleased electrons diffuse into the crystal and occupy
anionic sites. The anionic sites occupied by unpaired electrons are called F. These electrons
absorb some energy of white light, giving the yellow colour to NaCl. Similarly, excess of
lithium makes LiCl crystals pink and excess of potassium makes KCl crystals violet (or
lilac).
 Zinc oxide is white in colour at room temperature. On heating it loses oxygen and turns
yellow. [ZnO → Zn+2 + O-2 +2e-]
 The excess Zn2+ ions move to interstitial sites and the electrons to neighbouring interstitial
sites.
(46)One Ca2+ replaces two K+ units. 10-3 moles of Ca2+ will replace 2 × 10-3 moles of K+. Hence
cationic vacancies = 10-3 mole percent
(47) Ferromagnetic substances would make better permanent magnet. Because when
Ferromagnetic substances are placed in a magnetic field all the domains (act as a tiny

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magnet) get oriented in the direction of the magnetic field and a strong magnetic effect is
produced. This ordering of domains persists even when the magnetic field is removed.
While in ferrimagnetic substances, the net magnetic movement arise due to unequal
number of domains in opposite direction.
(48) Ferrimagnetic Fe3O4 on heating to 850 K becomes paramagnetic because on heating
there will be greater alignment of spins in one direction.
(49) 8 corner X (1/8) atom per unit cell = 1 atom
There are four body diagonals in a cubic unit cell and each has two body centre atoms. So 4
X 2=8 atoms therefore total number of atoms per unit cell =1+8=9
(50) Two Ag+ ions will be replaced by one Ca2+ ions to maintain electrical neutrality. Thus a
hole is created at the lattice site for every Ca2+ ion introduced.
(51) a=2 X √2r =2 X 1.414 X 0.144 nm =0.407 nm
(52) In metals with increase of temperature, the kernels start vibrating and thus offer
resistance to the flow of electrons. Hence conductivity decreases. In case of semi-
conductors, with increase of temperature, more electrons can shift from valence band to
conduction band. Hence conductivity increases.
(53) Let the M2+ ion in the crystal be x and M3+ = 0.98-x
Since total charge on the compound must be zero
2x+3(0.98-x)-2=0 then, X=0.88
% of M2+ = (0.88/0.96) X 100=91.67 &% of M3+ =100-91.67=8.33
(F) NCERT (NUMERICAL)
ZM 3 Z. M 2 x 92.91 −23 −24
(2)d= 3 &a = = =3.609 x 10 =36.09 x 10
a NA d . N A 6.022 x 10 x 8.55
23

−8
so,a=3.305 x 10 cm=330.5 pm
1.732 x 330.5
We know that, 4 r= √ 3 a or r = =143 pm
4
(3)a=5.78 X 10-8cm
(10) No. of moles of ‘k’ = 11.7/39 = 0.3
No. of atoms of ‘k’ = 0.3 x 6.022 x 1023
No. of atoms of ‘k’ per B.C.C. Unit Cell = 2
23
0.3 x 6.022 x 10 22
No. of Unit cells ¿ =9.03 x 10
2
ZxM 3
dxa xNA
(11)d= 3 or Z= = 7.2 x ¿ ¿= 2.011 = 2
a xNA M
Hence, the unit Cell is B.C.C.

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 3 3
(12) r  a 4.29 A

1.86 A 
4 4
(13)7.882g/cm3 (14)M = 52 g mol–1(15)2.715 g cm-3
3
(16)bySolution Z =2, It indicates that metal has bcc lattice. For bcc lattice, r  a
4
Or r = 2.165 x 102 = 216.5 pm
r
(17) For a tetrahedral void  0.225then, r+ = 0.225 × 195 = 80.735 pm
r
(18)For rock salt structure, when anion-cation contact is there along the cell edge,
r+ a
≈0.731 …….. (1) and r+ + r-= …….. (2)
r- 2
r- a 1 6.28 1
Dividing (2) with r+ then, 1 + = x or 1 + 1.368 = x
r+ 2 r+ 2 r+
Or r+ =1.326 A0
(19)One Ca2+ replaces two K+ unitsor10-3 moles of Ca2+ will replace 2 × 10-3 moles of K+.
Hence cationic vacancies = 10-3 mole percent
(20)10.5 g cm-3
(21)Volume of the unit cell = (288 pm)3 = (288×10-10 cm)3 = 2.39×10-23 cm3
 Volume of 208 g of the element:

 Number of unit cells in this volume :

 Since each bcc cubic unit cell contains 2 atoms, therefore, the total number of atoms in 208
g = 2 (atoms/unit cell) × 12.08 × 1023unit cells= 24.16×1023 atoms
(22)

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