1. Quantity of energy released when 1 mole of the ionic crystal is formed from gaseous ions is called:
(a) Bond energy
(b) Potential energy
(c) ionization energy
(d) Lattice energy
1. Explanation (Answer; d)
In the formation of ionic solids, oppositely charged gaseous ions brought closer to each other and arranged three dimensionally in certain pattern releasing a high amount of energy known as lattice energy which is the energy associated with electrostatic interaction between the ions in a crystal.
Lattice Energy is defined as the amount of energy released when gaseous ions of opposite charges combine to give one mole of a crystalline ionic compound. The energy liberated in this case will have a negative sign. It is expressed in kJ/mol.
2. Graphite can conduct electricity in one direction only. With this behavior, it is said
(a) amorphous
(b) Symmetrical
(c) anisotropic
(d) Polymorphous
2. Explanation (Answer; c)
the variation of intensity of certain physical properties (such as electrical conductivity, refractive index etc.) in different directions is called anisotropy and the substance possessing this property is called Anisotrope.
Graphite contains delocalized electrons (free electrons). These electrons can move through the graphite, carrying charge from place to place and allowing graphite to conduct electricity.
Anisotropy is the property of molecules or substances to exhibit variations in physical properties along different molecular axes of the substance and the substance possessing this property is called Anisotrope.
The property of a crystalline substance in which its crystal shows variable intensity of physical properties (such as coefficient of thermal expansion, electrical and thermal conductivity, refractive index etc.) in different directions in the crystal lattice is called Anisotropy and the substance possessing this property is called Anisotrope.
Crystalline solids are usually anisotropic and exhibit the property of anisotropy i.e. they have certain physical properties that vary with direction. Crystalline solids show variable intensity of physical properties in different directions. Their physical properties like electrical conductivity, thermal conductivity, thermal expansion, refractive index, mechanical strength etc. are different in different directions.
Reason of Anisotropic Behaviour
The reason of anisotropic attitude is attributed to the fact that arrangement of particles is different in the different directions.
For example:
Graphite can conduct electricity parallel to its plane of layers but not perpendicular to plane because of electron movement is not allowed on perpendicular of the layer.
3. NaCl and MgO are isomorphous solids because these have same:
(a) Melting point
(b) chemical properties
(c) geometrical shapes
(d) boiling pint
3. Explanation (Answer; c)
Two or more substances having the same crystal structure are said to be isomorphous (iso – same, morphous – form) solids and the phenomenon is called isomorphism.”
NaCl and MgO have the same geometrical shapes. Isomorphous substance usually have same atomic ratio, similar type of molecular formula but they have entirely different physical and chemical properties.
4. The temperature at which two allotropic forms co-exist in equilibrium is called as
(a) Melting temperature
(b) fusion temperature
(c) Transition temperature
(d) critical temperature
4. Explanation (Answer; c)
The allotropic forms of element have different stabilities and unstable variety changes into the stable allotropic form at a certain temperature called transition temperature which has fixed value for each pair of allotropes. Thus transition temperature is the temperature at which two crystalline forms of the same element co-exist in equilibrium with each other. (It exists both for allotropes and polymorphs).
It has been noticed that the transition temperature of two different crystalline forms of a substance is always less than its melting point.
5. Diamond is the example of:
(a) Ionic solid
(b) Covalent solid
(c) Metallic solid
(d) Molecular solid
5. Explanation (Answer; c)
Diamond is the example of covalent solid or Macromolecular or Covalent Network Solids or non-metallic crystals). The crystals which consist of atoms held together by covalent bonds are called Covalent Crystals . These are the solids consisting of atoms of the same or different elements connected to each other by network of covalent bonds throughout the crystal forming a giant molecule.
Examples of Covalent Network Solids
diamond, graphite, carbon, silicon, germanium, quartz (SiO2), corborundum or silicon carbide (SiC), BN, AlN, etc.
6. Ice is a molecular solid, the intermolecular force of attraction among its molecules
(a) ionic bond
(b) Covalent bond
(c) Metallic bond
(d) Hydrogen bond
6. Explanation (Answer; d)
Ice is a molecular solid, the intermolecular force of attraction among its molecules is hydrogen bond due to polar nature of water molecules in ice.
The crystals which consist of polar or non-polar molecules of a substance held together weak intermolecular forces either by hydrogen bonding or Vander Waal’s forces are called Molecular Crystals.
Examples molecular crystals
the polar and non-polar molecules such as Iodine, argon, S8, chlorine, ice, dry ice (solid CO2), sugar, glucose, methane, cholesterol, benzene, paraffin, ascorbic acid, hydroquinone, etc.
7. If all three axes in unit cell are of different length but all angles are of 90° then it is identified as:
(a) Orthorhombic system
(b) Hexagonal system
(c) Tetragonal system
(d) Cubic system
7. Explanation (Answer; a)
In orthorhombic System, all the three axes of unequal lengths at right angles to each other i.e. all angles are of 90°.
Examples of orthorhombic System
Rhombic sulphur, ZnSO4.7H2O, FeSO4.7H2O, MgSO4.7H2O, KNO3, CaCO3 (aragonite), BaSO4
8.In NaCl, each Na ion is surrounded by Cl ions in the numbers:
(a) Four
(b) Three
(c) Six
(d)Seven
8. Explanation (Answer; c)
The structure of sodium chloride crystal is built up be repeating face centred cubic unit cells. In crystallographic view point, each Na+ ion is surrounded by six Cl− ion and each Cl− ion is covered up with six Na+ ions. This ionic arrangement suggest that the coordination number of sodium chloride crystal is 12. Thus, in sodium chloride, Na+ as well as Cl– ions have the coordination number of 6.
9. It is an example of crystalline solid:
(a) Alum
(b) Glass
(c) Plastic
(d) Rubber
9. Explanation (Answer; a)
Alum is a crystalline solid.
glass, plastics, rubber (polymeric solids), cement, polymers, talc powder, charcoal, tar, soot, resins, gel, amorphous silica (one of the best material for converting sunlight into electricity; photovoltaic cell), etc.
10.Each unit cell of sodium chloride consists of:
(a) Eight Na and Eight Cl ions
(b) Two Na & Two Cl ions
(c) Four Na &Four Cl ions
(d) Four Na & Six Cl ions
10. Explanation (Answer; c)
NaCl has a cubic crystal system and a face-centered cubic crystalline structure. The structure of sodium chloride consists of eight ions a unit cell, four are Na+ ions and the other four are Cl– ions i.e. NaCl has four cations and four anions in a face-centered cubic unit cell.
Since there are 4 atoms or ions present in each unit cell of a face centred cubic structure, therefore, the number of NaCl units in a unit cell of NaCl is four.
11. Which one of the following does not have same chemical properties?
(a) Isomorphs
(b) Polymorphs
(c) Allotropes
(d) Isotopes
11. Explanation (Answer; a)
Isomorphs ……have different chemical properties due to different chemical formulae.
Polymorphs.... have same chemical properties due to same chemical composition.
Allotropes…… have same chemical properties due to same chemical nature.
Isotopes……… have same chemical properties due to same atomic number.
12. Which element does not show allotropy?
(a) Carbon
(b) Sulphur
(c) Nitrogen
(d) Oxygen
12. Explanation (Answer; c)
Nitrogen and bismuth in group VA does not show allotropy.
13. In case of element, the polymorphic forms are called
(a) Isomorphs
(b) Isomers
(c) Allotropes
(d) Isotopic forms
13. Explanation (Answer; c)
the polymorphic forms are called allotropes in case of elements.
14. Which one is an amorphous solid?
(a) Glass
(b) Rubber
(c) Plastic
(d) All of them
14. Explanation (Answer; d)
glass, plastics, rubber (polymeric solids), cement, polymers, talc powder, charcoal, tar, soot, resins, gel, amorphous silica (one of the best material for converting sunlight into electricity; photovoltaic cell), etc.
15. The temperature at which two crystalline forms of the same substance can co-exist in equilibrium with each other is called?
(a) Standard temperature
(b) Equilibrium temperature
(c) Transition temperature
(d) Absolute temperature
15. Explanation (Answer; c)
The temperature at which two crystalline forms of the same substance can co-exist in equilibrium with each other is called Transition temperature.
The allotropic forms of element have different stabilities and unstable variety changes into the stable allotropic form at a certain temperature called transition temperature which has fixed value for each pair of allotropes. Thus transition temperature is the temperature at which two crystalline forms of the same element co-exist in equilibrium with each other. (It exists both for allotropes and polymorphs).
It has been noticed that the transition temperature of two different crystalline forms of a substance is always less than its melting point.
16. Which one of the following is a super-cooled liquid?
(a) Glass
(b) Ice
(c) Dry ice
(d) None of them
16. Explanation (Answer; a)
Glass is a super-cooled liquid and amorphous solid. It is also called pseudo solid.
17. Which one of the following does not have cubic crystal?
(a) Graphite
(b) Diamond
(c) NaCl
(d) NaF
17. Explanation (Answer; a)
Graphite has hexagonal crystal.
18. Which one of the following has rhombohedral crystal?
(a) Graphite
(b) Diamond
(c) Ice
(d) NaF
18. Explanation (Answer; c)
Ice has rhombohedral crystal.
19. The crystals in which molecules are held together by van der Waal’s forces are called:
(a) Ionic crystals
(b) Molecular crystals
(c) Metallic crystals
(d) All of them
19. Explanation (Answer; b)
Molecular crystals consists of molecules which are held together by van der Waal’s forces.
20. Which one is not an example of molecular crystals?
(a) Ice
(b) Dry ice
(c) NaCl
(d) Iodine
20. Explanation (Answer; c)
NaCl forms ionic crystals.
21. The crystals in which non-metallic atoms are held together in a network of single covalent bonds are called:
(a)Ionic crystals
(b) Molecular crystals
(c) Metallic crystals
(d) Covalent crystals
21. Explanation (Answer; d)
Covalent crystals consist of non-metallic atoms are held together in a network of single covalent bonds.
22. Which one the following is NOT an example of covalent crystals?
(a) Diamond
(b) Graphite
(c) Silver
(d) Silica
22. Explanation (Answer; c)
Silver is a metal and it forms metallic crystals.
23. Which one is an example of metallic crystals?
(a) Molybdenum
(b) Zirconium
(c) Copper
(d) All of them
23. Explanation (Answer; d)
All are the examples of metallic crystals.
24. Which one is an example of ionic crystals?
(a) Graphite
(b) Dry ice
(c) KCl
(d) Iodine
24. Explanation (Answer; c)
Ionic crystals usually contain Na, K, Ca, Mg, Ba along with Cl, Br, I, O, S, N, SO42−, NO3−, etc.
25. Which one of the following crystals will conduct electricity?
(a) Metallic crystals
(b) Solid ionic crystals
(c) Molecular crystals
(d) Covalent crystals
25. Explanation (Answer; a)
Metallic crystals are electrical conductors due to the presence of free electrons.
26. Array of points which show how the constituent particles of a crystal are arranged at different sites in three-dimensional space is called
(a) Space lattice
(b) Lattice array
(c) Crystal lattice
(d) All of them
26. Explanation (Answer; d)
Crystal lattice or Space lattice or Lattice array is the Array of points which show how the constituent particles of a crystal are arranged at different sites in three-dimensional space
27. The transition temperature of tin is
(a) 13.2oC
(b) 95.5oC
(c) 128oC
(d) None of these
27. Explanation (Answer; d)
28. The smallest unit of volume of a crystal which when repeated in three dimensions can generate the structure of the entire crystal is called a:
(a) Crystal lattice
(b) Unit cell
(c) Crystal
(d) None of the above
28. Explanation (Answer; b)
Unit cell is the basic and smallest structural unit of a crystal when repeated in three dimensions can generate the structure of the entire crystal.
29. Lattice energy is also called:
(a) Enthalpy
(b) Ionization energy
(c) Activation energy
(d) Crystal energy
29. Explanation (Answer; d)
Lattice energy is also called Crystal energy.
30. In molecular crystals, molecules are held together through:
(a) Metallic bond
(b) van der Waal’s forces
(c) Electrostatic forces
(d) Covalent bond
30. Explanation (Answer; b)
In molecular crystals, molecules are held together through van der Waal’s forces either through London dispersion forces or dipole-dipole forces or hydrogen bonding.
31. Diamond forms which type of crystal system?
(a) Regular
(b) Hexagonal
(c) Trigonal
(d) Triclinic
31. Explanation (Answer; d)
Diamond forms regular or cubic crystal.
32. If all the axes are equal at right angles to one another, then crystal is called:
(a) Tetragonal
(b) Trigonal
(c) Cubic
(d) Triclinic
32. Explanation (Answer; c)
Cubic crystals are characterized by all the equal axes at right angles to one another.
33. What is the co-ordination number of sodium ion in the sodium chloride lattice?
(a) 1
(b) 2
(c) 4
(d) 6
33. Explanation (Answer; d)
The number of ions of same kind that surround an oppositely charge ion is called coordination number. The structure of sodium chloride crystal is built up be repeating face centred cubic unit cells.
In crystallographic view point, in NaCl, each Na+ ion is surrounded by six Cl− ion and each Cl− ion is covered up with six Na+ ions. This ionic arrangement suggest that the coordination number of sodium chloride crystal is 6. The coordination number of Na+ is 6 and coordination number of Cl− is also 6.
34. Which type of hybridization is found in carbon in graphite?
(a) sp3
(b) sp2
(c) sp
(d) None of the above
34. Explanation (Answer; b)
Since in graphite, each carbon is bonded by three other carbons, each carbon must be sp2-hybridized (AB3).
35. Which one is not isotropic?
(a) Gases
(b) Liquids
(c) Crystalline solids
(d) Amorphous solids
35. Explanation (Answer; d)
All gases, true liquids and amorphous solids are isotropic, meaning that their properties are uniform in all directions— the result of their molecules being in constant random motion. Crystalline solids, in contrast, are anisotropic; optical- and other properties such as thermal and electrical conductivity vary with direction.
36. Which one of the following does have same chemical properties?
(a) Isotopes
(b) Allotropes
(c) Polymorphs
(d) All of the above.
36. Explanation (Answer; d)
Isotopes have same chemical properties due to same atomic number and hence same electronic configuration.
Allotropes have same chemical properties due to same elemental composition.
Polymorphs have chemical properties due to same chemical composition or chemical formula.
37. Which one is good conductor of electricity?
(a) Diamond
(b) Graphite
(c) Sugar
(d) Dry ice
37. Explanation (Answer; b)
Diamond being a covalent crystal is non-conductor.
Sugar and dry ice being molecular solids are non-conductor.
Graphite inspite of covalent crystal is a good conductor due to the presence of free electrons owing to sp2-hybridization of carbon.
38. Which one of the following elements does not show allotropy?
(a) Tin
(b) Sulphur
(c) Oxygen
(d) Bismuth
38. Explanation (Answer; d)
The two elements of VA group namely nitrogen and bismuth do not show allotropy.
39. Which crystalline allotrope of carbon conducts electricity?
(a) Graphite
(b) Diamond
(c) Coke
(d) Lamp black
39. Explanation (Answer; a)
Graphite, a crystalline allotrope of carbon inspite of covalent crystal is a good conductor due to the presence of free electrons owing to sp2-hybridization of carbon.
40. The force of attraction between positive metal ions and Electron Sea is called?
(a) Metallic bond
(b) Hydrogen bond
(c) Electrostatic force
(d) London force
40. Explanation (Answer; a)
Metallic bond the electrostatic force of attraction between positive metal ions (kernels) and electron sea.
41. At which temperature both rhombic and monoclinic forms of sulphur exist in equilibrium with each other:
(a) 18°C
(b) 32°C
(c) 96.5°C
(d)95.5°C
41. Explanation (Answer; c)
Transition temperature is the temperature at which two crystalline forms of the same substance can co-exist in equilibrium with each other. (It exists both for allotropes and polymorphs).
It has been noticed that the transition temperature of two different crystalline forms of a substance is always less than its melting point.
The transition temperature of rhombic and monoclinic forms of sulphur 95.5°C.
42. The formula of corborundum is:
(a) SiC
(b) CaC2
(c) Al4C3
(d) SiO2
42. Explanation (Answer; a)
The formula of corborundum or silicon carbide is SiC (both Si and C are tetravalent giving AB type formula).
43. Quartz forms which type of crystal?
(a) Ionic
(b) Metallic
(c) Covalent
(d) Non-metallic
43. Explanation (Answer; c)
Quartz forms covalent crystal.
44. Transition temperature only exists for:
(a) Elements
(b) Compounds
(c) Mixtures
(d) Both a and b
44. Explanation (Answer; d)
Transition temperature exists both for allotropes (elements) and polymorphs (compounds).
45. The coordination number of Y will be in the XY types of crystal:
(a) 4
(b) 8
(c) 12
(d) 6
45. Explanation (Answer; d)
The coordination number of Y will be in the XY types of crystal is 6.
46. Which one of the following is not a macromolecular solid?
(a) Diamond
(b) Quartz
(c) Naphthalene
(d) Corborundum
46. Explanation (Answer; c)
Naphthalene being non-polar forms molecular crystals.
47. Which one of the following is not a sublime solid?
(a) Camphor
(b) Ice
(c) Naphthalene
(d) Dry ice
47. Explanation (Answer; b)
Ice is normal solid.
48. Isomorphous substances have same:
(a) Chemical properties
(b) Physical properties
(c) Empirical formula
(d) Density
48. Explanation (Answer; c)
Isomorphous substances have same empirical formula or atomic ratio.
49. Which one of the following crystals will conduct electricity?
(a) Covalent crystals
(b) Solid ionic crystals
(c) Molecular crystals
(d) None of them
49. Explanation (Answer; d)
Only molten or aqueous ionic crystals or metallic crystals are conductor.
50. LiF is a/an………… crystal.
(a) Covalent
(b) ionic
(c) Molecular
(d) metallic
50 Explanation (Answer; b)
LiF is an ionic crystal.
51. In solid ice, molecules are held together through:
(a) Metallic bond
(b) van der Waal’s forces
(c) Electrostatic forces
(d) Covalent bond
51. Explanation (Answer; b)
Solid ice forms molecular crystals held together by van der Waal’s forces (hydrogen bonds).
52. Which of the following is a crystalline solid?
(a) Tar
(b) Butter
(c) Sucrose
(d) Glass
52. Explanation (Answer; c)
Sucrose is a crystalline solid having definite geometrical shape (monoclinic).
53. Which of the following pair of compounds is NOT isomorphous?
(a) NaF and MgO
(b) NaNO3 and CaCO3
(c) K2SO4 and K2SeO4
(d) NaCl and KCl
53. Explanation (Answer; d)
lsomorphous substances generally have similar crystal structure and chemical formulae and their polarizability and the ratio of cation and anion radii are usually identical. Among the given pair of compounds, NaCl and KCI are not isomorphous because they have different crystal structures.
54. Which of the following is not a property of crystalline solid?
(a) Isotropy
(b) Anisotropy
(c) Sharp melting point
(d) Definite geometry
54. Explanation (Answer; a)
Isotropy is the property of amorphous solids, liquids and gases.
55. Which one is not isotropic?
(a) He
(b) Water
(c) Minerals
(d) Plastics
55. Explanation (Answer; c)
Crystalline solids (like minerals) are anisotropic.
56.Odour of common household naphthalene balls and para-dichlorobenzene(bath room deodorizer) is due to:
(a) Effusion
(b) Sublimation
(c) Diffusion
(d) Deposition
56. Explanation (Answer; b)
naphthalene balls and para-dichlorobenzene(bath room deodorizer) are sublime in nature.
57. In the unit cell of NaCl lattice, there are _______.
(a) 3 Na+ ions
(b) 6 Na+ ions
(c) 6 Cl– ions
(d) 4 NaCl units
57. Explanation (Answer; d)
The number of NaCl units present in a unit cell of NaCl is 4. NaCl crystallizes in fcc structure. A fcc structure contains 4 atoms/ions/molecules per unit cell.
58. Which type of solid conduct electricity in molten state but not in solid state?
(a) Covalent
(b) Ionic
(c) Metallic
(d) Network
58. Explanation (Answer; b)
Ionic solids conduct electricity in molten state due to availability of mobile ions but they are non-conducting in solid state due to fixed positions of ions in the crystal lattice.
59. Nature of binding forces present in carbon dioxide molecules in solid state are
(a) Hydrogen bonding
(b) Electrostatic forces
(c) London forces
(d) Metallic forces
59. Explanation (Answer; c)
Solid carbon dioxide is called dry ice which forms molecular crystals in which its molecules are held together by London forces as carbon dioxide is non-polar.
60. Which type of interaction hold the molecules together in a polar molecular solids?
(a) Metallic bonding
(b) Dipole-dipole interaction
(c) London forces
(d) Hydrogen bonding
60. Explanation (Answer; b)
Polar molecular solids are held together by Dipole-dipole interaction.
61. Giant ionic structures is also a name given to
(a) Ionic lattice
(b) Crystal lattice
(c) Metallic lattice
(d) Covalent lattice
61. Explanation (Answer; a)
Giant ionic structures is also a name given to Ionic lattice.
62. Which one of the following shows more than one kind of chemcial bonding?
(a) Brass
(b) Copper
(c) Diamond
(d) Ice
62. Explanation (Answer; d)
Brass and copper contain metallic bonding only.
Diamond contains covalent bonding only
Ice contains covalent and hydrogen bonding.
63. Repeatable entity of a crystal structure is known as
(a) Lattice
(b) Unit cell
(c) Crystal
(d) None of them
63. Explanation (Answer; b)
Unit cell or unit crystal is the smallest basic repeating structural unit of a crystalline solid (crystal) possessing a definite geometrical shape containing number of atoms, ions or molecules and showing all the characteristics of actual crystal.
A unit cell is formed by the arrangement of atoms, molecules or ions in three dimensional space and showing all the characteristics of actual crystal. These unit cells repeat itself in three dimensions in definite pattern to form the crystal.
64. In NaCl type structure, the coordination number of cation and anions are
(a) 8 and 4
(b) 4 and 4
(c) 6 and 4
(d) 6 and 6
64. Explanation (Answer; d)
In the crystal structure of NaCl, there are 6 anions around each cation (coordination number Na = 6 ); Because of the 1:1 stoichiometry there must also be 6 Na cations around each Cl anion.
Thus coordination number of NaCl will be 6:6
Each Na+ ion has a Cl– neighbour below and above, towards the right and the left, and the front and the back in the NaCl structure. The same holds for Cl– ion. The coordinating number for both ions is 6. In a crystal of NaCl, each sodium atom is surrounded by 6 chloride ions, so each ion of chloride is encircled by 6 sodium ions. As a consequence, the coordination amount of NaCl would be defined as 6:6.
65. Which solids are called true solids?
(a) Amorphous
(b) Crystalline
(c) Metallic
(d) Ionic
65. Explanation (Answer; b)
Crystalline solids are called true solids as the atoms, ions or molecules are arranged in an ordered and symmetrical pattern that is repeated over the entire crystal.
66. Which of the following substances is not amorphous?
(a) Silver nitrate
(b) Rubber
(c) Polymers
(d) Glass
66. Explanation (Answer; a)
Silver nitrate is a crystalline solid.
67. Which one of the following is a poor conductor of electricity?
(a) Metallic crystals
(b) ionic crystals
(c) Molecular crystals
(d) Graphite
67. Explanation (Answer; c)
Molecular crystals are poor conductor of electricity due to absence of mobile ions or free electrons. Ionic crystals are poor conductor of electricity in solid state but in aqueous solution or molten state, they are conductor or electrolyte and conduct electricity.
68. In diamond, the carbon atoms are arranged in a
(a) Tetrahedral manner
(b) Square planar manner
(c) Hexagonal manner
(d) None of them
68. Explanation (Answer; a)
In diamond, the carbon atoms are sp3 hybridized and arranged in a tetrahedral manner.
69. How many Cl− ions are there around Na+ ion in NaCl crystal?
(a) 3
(b) 4
(c) 6
(d) 8
69. Explanation (Answer; c)
In the crystal structure of NaCl, there are 6 anions around each cation (coordination number Na = 6 ); Because of the 1:1 stoichiometry there must also be 6 Na cations around each Cl anion.
Thus coordination number of NaCl will be 6:6
70. Among solids, the highest melting point is exhibited by
(a) Ionic solids
(b) Molecular solids
(c) Covalent solids
(d) Pseudo solids
70. Explanation (Answer; c)
The order of melting points of different types of solids is
Covalent solids > Ionic solids > Molecular solids > pseudo solids
Covalent solids also called network solids are solids that are held together by covalent bonds in three dimensional network. As a result, the melting points of covalent solids is extremely high.
71. Which of the following is a crystalline solid?
(a) Tar
(b) Butter
(c) Sugars
(d)Glass
71. Explanation (Answer; c)
Sugars are crystalline solids.
72. Covalent solids are composed of
(a) Ions
(b) Different molecules
(c) Neutral atoms
(d) Any of the above
72. Explanation (Answer; c)
Covalent solids are composed of Neutral atoms forming giant macromolecules.
73. Carbon atoms of diamond are
(a) sp hybridized
(b) sp3 hybridized
(c) sp2 hybridized
(d) Unhybridized
73. Explanation (Answer; b)
Carbon atoms of diamond are sp3 hybridized as carbon is covalently bonded to 4 other carbon atoms.
74. Ionic crystals are
(a) Hard
(b) Soft
(c) Amorphous
(d) Brittle
74. Explanation (Answer; d)
Ionic crystals are brittle.
75. Molecular crystals are generally
(a)Hard
(b) Unstable
(c) Soft
(d) Stable
75. Explanation (Answer; c)
Molecular crystals are generally soft due to weak van der Waal’s forces.
76. The unit cell with the following structure refers to ………… crystal system.
(a) Cubic
(b) Trigonal
(c) Tetragonal
(d) Orthorhombic
76. Explanation (Answer; )
Orthorhombic System; a ≠ b ≠ c, α = β = γ = 90° e.g. Rhombic sulphur
77. Sugar shows one the following crystalline system?
(a) Tetragonal
(b) Rhombohedral
(c) Triclinic
(d) Monoclinic
77. Explanation (Answer; d)
Sugar shows one the Monoclinic crystalline system
78. Which of the following solids show anisotropy?
(a) Glass
(b) Rubber
(c) Plastic
(d) None of the above
78. Explanation (Answer; d)
All the given options contain amorphous solids which are isotropic.
79. In solids, the temperature is the measure of
(a) Average KE
(b) Vibrational KE
(c) Translational KE
(d) None of the above
79. Explanation (Answer; b)
In solids, the temperature is the measure of Vibrational KE.
80. Each unit cell of NaCl consists of 4 chloride ions and _______.
(a) 13 Na atoms
(b) 4 Na+ ions
(c) 6 Na atoms
(d) 8 Na atoms
80. Explanation (Answer; b)
Each unit cell of NaCl consists of 4 chloride ions and 4 Na+ ions.
81. Which of the following has only London dispersion forces?
(a) Water
(b) NaCl crystal
(c) NH3 gas under high pressure
(d) Liquefied argon
81. Explanation (Answer; d)
Noble gases in liquefied form only has London dispersion forces. Liquefied argon being non-polar has London dispersion forces.
82. A solid has a sharp melting point slightly above room temperature and is a poor thermal and electrical conductor. Its crystal classification on the basis of bonding is
(a) Metallic
(b) Molecular
(c) Ionic
(d) Covalent
82. Explanation (Answer; b)
Low melting point and Poor thermal and electrical conductivity is the characteristic of molecular solids.
83. The space lattice of graphite is
(a) Tetragonal
(b) Hexagonal
(c) Rhombic
(d) Cubic
83. Explanation (Answer; b)
The space lattice of graphite is Hexagonal.
84. Solid CH4 is
(a) covalent solid
(b) Molecular solid
(c) ionic solid
(d) Metallic solid
84. Explanation (Answer; c)
Solid CH4 being non-polar forms molecular solid.
85. An example of a covalent crystalline solid is
(a) Al
(b) Ar
(c) Si
(d) NaF
85. Explanation (Answer; c)
An example of a covalent crystalline solid is silicon.
86. Among solids, the highest melting points is exhibited by
(a) Pseudo solids
(b) Metallic solids
(c) Molecular solids
(d) Ionic solid
86. Explanation (Answer; d)
Among solids, the highest melting points is exhibited by Ionic solid.
87. Iodine molecules are held together in the crystals lattice by
(a) Dipole-dipole forces
(b) Covalent bonds
(c) London forces
(d) Coulombic forces
87. Explanation (Answer; c)
Iodine being non-polar forms molecular crystals in which iodine molecules are held together by London forces.
88. How many three-dimensional crystal lattices are possible?
(a) 7
(b) 14
(c) 20
(d) 3
88. Explanation (Answer; b)
There are total 14 three-dimensional crystal lattices.
89. Which is covalent solid?
(a) Ice
(b) Dry ice
(c) Sugar
(d) None of them
89. Explanation (Answer; d)
All the given options contain molecular solids.
90. Solids are characterized by their properties......
(a) crystalline nature
(b) incompressibility
(c) mechanical strength
(d) all of the above
90. Explanation (Answer; d)
All are the characteristic properties of solids.
91. The inter particle forces in solid hydrogen are...
(a) coordinate bonds
(b) hydrogen bonds
(c) van der Waal’s forces
(d) covalent bonds
91. Explanation (Answer; c)
The inter particle forces in solid hydrogen are van der Waal’s forces as hydrogen is non-polar.
92. The number of carbon atoms per unit cell of diamond unit cell is
(a) 6
(b) 4
(c) 2
(d) 8
92. Explanation (Answer; d)
Diamond has FCC lattice structure and it is built by carbon atoms. Here carbon atoms occupies the corners, face centers and also half of the tetrahedral voids.
Therefore number of carbon atoms per unit cell
= 8× 1/8 (Corners) + 6×½ (Face centered) + 8× ½ (Tetrahedral void) = 8
93. London dispersion forces are more significant at
(a)High temperature
(b) Low temperature
(c) High pressure
(d) Both a and c
93. Explanation (Answer; d)
London forces become more prominent when molecules are close each other. Low temperature and high pressure decreases intermolecular distance thereby increasing attractive forces among molecules in the form of strong London forces.
94. Crystalline solids have different properties:
(I) Allotropy (II) Isomorphism (III) Polymorphism
Ionic compounds show which of the above properties?
(a) I and II only
(b) II and III only
(c) I and III only
(d) I, II and III
94. Explanation (Answer; b)
Ionic compounds cannot show allotropy as it the property of an element. Isomorphism and polymorphism are property of compounds
95. The unit cell of NaCl contains ………….. formula units
(a) 8
(b) 4
(c) 6
(d) 2
95. Explanation (Answer; b)
The number of NaCl units present in a unit cell of NaCl is 4. NaCl crystallizes in fcc structure. A FCC structure contains 4 atoms/ions/molecules per unit cell.
Since sodium chloride have a face-centered cubic (FCC) structure therefore,
No of particles at one corner=1÷8
No of particles at all corners=1÷8 × 8= 1
(we multiplied 8 because cube have 8 corners!)
No of particles at one Face = 1÷2
No of particles at all 6 faces =1÷2 × 6=3
Total no. of particles in FCC = number of particles at all 8 corners + number of particles at all 6 faces ⇒ 1 + 3 = 4
Hence one unit cell of sodium chloride crystal contains 4 NaCl (formula units)
96. The lattice energy of LiCl is …………… kJmol‒1.
(a)−690
(b) −728
(c) -895
(d) -883
96. Explanation (Answer; a)
The lattice energy of LiCl is -883 kJmol‒1.
97. Coordination number of “Cs” in “CsCl” is
(a) 2
(b) 4
(c) 6
(d) 8
97. Explanation (Answer; d)
Coordinating number of “Cs” in “CsCl” is 8
In CsCl, cesium ions form the simple cubic arrangement and chloride ions occupy the interstitial sites such that each cesium ion is surrounded by 8 chloride ion and each chloride ion is surrounded by 8 cesium ion. So, coordination is 8:8.
98.On the basis of symmetry, the crystals have been divided into ………..types.
(a) 14
(b) 7
(c) 9
(d) 3
98. Explanation (Answer; d)
On the basis of symmetry, the crystals have been dividied into 3 types; plane of symmetry, axis of symmetry and center of symmetry.
99. An example of ion-dipole forces is
(a) Bromine in benzene
(b) Ethanol in water
(c) Sugar in water
(d) NaCl in water
99. Explanation (Answer; d)
NaCl being an ionic compound and water being a polar compound set up an electrostatic force between ions of salt and dipoles of water which is called ion-dipole force.
100 In unit cell, the angle between the faces b and c is
(a) α
(b) β
(c) γ
(d) All of these
100. Explanation (Answer; a)
In unit cell, the angle between the faces b and c is α.
101. Naphthalene is soluble in carbon tetrachloride due to:
(a) London dispersion forces
(b) Hydrogen bonding
(c) Dipole-induced dipole force
(d) Dipole-dipole forces
101. Explanation (Answer; a)
London dispersion forces are present in non-polar molecules. Naphthalene and carbon tetrachloride being non-polar, developing London forces.
102. Which of the following is an example of molecular solid?
(a) Sodium sulphate
(b) Aluminium nitride
(c) Glucose
(d) Graphite
102. Explanation (Answer; d)
Glucose being a covalent compound forms molecular crystals.
103. The transition temperature of KNO3 is
(a) 95.5οC
(b) 32.02οC
(c) 32.38οC
(d) 128.5οC
103. Explanation (Answer; d)
104. The lattice energy is maximum for
(a) NaF
(b) KF
(c) CaF2
(d) MgF2
104. Explanation (Answer; d)
The lattice energy is maximum for MgF2 due to its small size and high charge density.
105. Which one of the following solid has the lowest melting point?
(a) Fe
(b) I2
(c) NaCl
(d) C6H12O6
105. Explanation (Answer; b )
Molecular solids have least melting point due to weakest attractive forces in the form of van der Waal’s forces. Iodine forms molecular crystals.
106. These are the solids in which three dimensional arrangement of molecules, atoms or ions is characteristic, regular and repetitive having characteristic geometrical shape:
(a) Amorphous solids
(b) Crystalline solids
(c) Metallic solids
(d) All of the above
106. Explanation (Answer; b )
Crystalline solids are characterized by regular, highly ordered repetitive three-dimensional arrangement of particles with characteristic geometrical shape.
107. These are the solids in which three-dimensional arrangement of molecules, atoms or ions is random and non-repetitive having no characteristic geometrical shape:
(a) Amorphous solids
(b) Crystalline solids
(c) Metallic solids
(d) All of the above
107. Explanation (Answer; a)
Amorphous solids are characterized by non-regular, random and non- repetitive three-dimensional arrangement of particles with no characteristic geometrical shape.
108. The breakage of big crystal into smaller crystals of identical shape is called:
(a) Crystallization
(b) Anisotropy
(c) Cleavage
(d) Allotropy
108. Explanation (Answer; c)
The breakage of big crystal into smaller crystals of identical shape is called Cleavage
109. The variation of certain physical properties in different directions is called:
(a) Crystallization
(b) Anisotropy
(c) Cleavage
(d) Allotropy
109. Explanation (Answer; b)
Anisotropy is the variation of certain physical properties in different directions of crystal.
110. The existence of two different substances in the same crystalline form is called:
(a) Polymorphism
(b) Isomorphism
(c) Isotrophism
(d) Isotopy
110. Explanation (Answer; b)
Isomorphism is the existence of two different substances in the same crystalline form
111. In a face centred cubic lattice, a unit cell is equally shared by how many faces?
(a) 8
(b) 4
(c) 2
(d) 6
111. Explanation (Answer; d)
In a face centred cubic lattice, a unit cell is equally shared by 6 faces.
All the faces of the face-centered unit cell are shared by 6 unit cells.
4 face are covered by 4 unit cells as shown in figure. The front and back face are also covered by 2 unit cell.
⇒ Total of 6 unit cells
112. The existence of a substance in more than one crystalline forms under different conditions is called:
(a) Isotrophism
(b) Polymorphism
(c) Allotropy
(d) Isotopy
112. Explanation (Answer; b)
The existence of a substance in more than one crystalline forms under different conditions is called Polymorphism.
113. A single substance that crystallizes in two or more different forms under different conditions is said to be:
(a) Isomorphous
(b) Polymorphous
(c) Allotropes
(d) Isotropic
113. Explanation (Answer; )
A Polymorphous substance crystallizes in two or more different forms under different conditions
114. The existence of an element in more than one crystalline forms is called:
(a) Crystallization
(b) Anisotropy
(c) Cleavage
(d) Allotropy
114. Explanation (Answer; d)
Allotropy is the existence of an element in more than one crystalline forms
115. The different crystalline forms of the same element are called:
(a) Isomorphous
(b) Polymorphous
(c) Allotropes
(d) Isotropic
115. Explanation (Answer; c)
Allotropes are the different crystalline forms of the same element.
116. The coordination number of Y will be:
(a) 6
(b) 8
(c) 12
(d) 4
116. Explanation (Answer; d)
The given figure is a ZnS type structure.
In this structure, X is surrounded by 4 Y atoms, and each Y is surrounded by 4 X.
117. The coordination number of cation in crystal CsCl will be________.
(a) 6
(b) 8
(c) 12
(d) 4
117. Explanation (Answer; b)
Radius of Cs+ = 1.69Å
Radius of Cl−=1.81 Å
Radius ratio= rcs+/ rcl− = 1.69/1.81 = 0.933
When radius ratio is in the range (0.732−1), coordination no.=8
Limiting radius Ratio for predicting the shape of Ionic Solids
118. Coordination number of Cs+ and Cl− in CsCl crystal are:
(a) 8,8
(b) 4,4
(c) 6,6
(d) 8,4
118. Explanation (Answer; a)
In CsCl, cesium ions form the simple cubic arrangement and chloride ions occupy the interstitial sites such that each cesium ion is surrounded by 8 chloride ion and each chloride ion is surrounded by 8 cesium ion. So, coordination is 8:8.
119. If the radius of Mg2+ ions, Cs+ ion, O2− ion, S2− ion and Cl− ion are 0.65 Å , 1.69 Å , 1.40 Å , 1.84Å and 1.81 Å
respectively. The co-ordination numbers of the cations in the crystals of MgS, MgO and CsCl are, respectively :
(a) 4,8,6
(b) 6,4,8
(c) 8,4,6
(d) 4,6,8
119. Explanation (Answer; d)
120.In ionic solids, the arrangement of ions depends on _______.
(a) sizes of cations and anions
(b) the charges on the ions
(c) polarisability of anion
(d) all of these
120. Explanation (Answer; d)
In ionic solids, the arrangement of ions depends on all the given factors.
121.Amorphous substances have _______.
(i) definite heat of fusion
(ii) only short range order
(iii) only long range order
(iv) indefinite heat of fusion
(a) (i) and (iii) are correct
(b) (ii) and (iii) are correct
(c) (iii) and (iv) are correct
(d) (ii) and (iv) are correct
121. Explanation (Answer; d)
Amorphous substance have only short range order and indefinite heat of fusion.
122. The most symmetrical crystal system has the following unit cell dimensions:
(a) a = b = c and α = β = ϫ = 90ο
(b) a ≠ b ≠ c and α ≠ β ≠ ϫ ≠ 90ο
(c) a ≠ b ≠ c and α ≠ β ≠ ϫ = 90ο
(d) a = b = c and α = β = ϫ = 80ο
122. Explanation (Answer; a)
a = b = c and α = β = ϫ = 90ο
123. NaCl and CsF have same geometry because
(a) Their cations belong to group IA
(b)Their anions belong to group VIIA
(c) Both are soluble in water
(d) They have similar radius ratio
123. Explanation (Answer; d)
The geometry of ionic compounds depends upon the radius ratio of cation and anion. If two or more compounds have same radius ratio then they would have same geometry. NaCl and CsF have same geometry because they have similar radius ratio.
124. Isomorphic cyrstals show
(a) Same crystalline forms
(b) Same chemical properties
(c) Same physical properties
(d) Same melting properties
124. Explanation (Answer; a)
Isomorphic cyrstals have same crystalline forms. They have same atomic ratio or empirical formula.
125. As a substance moves from a solid to a liquid, all of the following changes occur except
(a) Molecules become more disordered
(b) KE of the molecules decrease
(c) Intermolecular forces become weaker
(d) Molecules move more frequently
125. Explanation (Answer; b)
The transition from solid to liquid is characterized by
(i) increasing entropy or more disordered
(ii) decreasing intermolecular forces
(iii) increasing molecular motion due to increasing KE
Hence transition from solid to liquid, KE of the molecules increases.
126. Isomorphous substances have
(a) Same physical and chemical properties
(b) Different physical and chemical properties
(c) Different physical and same chemical properties
(d) Same physical and different chemical properties
126. Explanation (Answer; b)
Isomorphous substances being different compounds have entirely different physical and chemical properties.
127. As solid melts to form liquid:
(a) Inter particle distance increases
(b) Inter molecular forces of attraction decreases
(c) Compressibility increases
(d) All of the above
127. Explanation (Answer; d)
The transition from solid to liquid is characterized by
(i) increasing inter-particle distance
(ii) decreasing intermolecular forces
(iii) increasing compressibility due to increasing increased inter particle distance.
128. Amorphous substances possess
(a) No definite geometry
(b) No definite heat of fusion
(c) No sharp melting points
(d) All of the above
128. Explanation (Answer; d)
All the given properties are characteristic of amorphous substances.
129. Which of the following are the CORRECT axial distances and axial angles for rhombohedral system?
(a) a = b = c, α = β = γ ≠ 90°
(b) a = b ≠ c, α =β = γ = 90°
(c) a ≠ b ≠ c, α = β = γ = 90°
(d)a ≠ b ≠ c, α ≠ β ≠ γ ≠ 90°
129. Explanation (Answer; a)
Trigonal/Rhombohedral System; a = b = c, α = = γ ≠ 90° (>90° <120°) e.g. Ice, calcite
130. The boiling point of iodine is far more greater than that of fluorine due to
(a) Strong London dispersion forces
(b) Greater polarizability
(c) Greater electronegativity of iodine
(d) Both a and b
130. Explanation (Answer; d)
Iodine is non-polar molecular solid. In molecular solid, the only binding force is London dispersion forces. The strength of London dispersion forces depends upon the polarizability which in turn depends upon the size and number of atoms (atomicity). Since iodine has greater atomic size than fluorine, iodine has greater polarizability and strong London dispersion forces.
131. The molecules of polar molecular solids are held together by _______.
(a) dipole-dipole interactions
(b) London dispersion forces
(c) Hydrogen bonds
(d) Both a and c
131. Explanation (Answer; d)
The molecules of polar molecular solids are held together by either dipole-dipole interactions or hydrogen bonds.
132. A crystalline solid _______.
(a) changes abruptly from solid to liquid when heated
(b) has no definite melting point
(c) undergoes deformation of its geometry easily
(d) has an irregular 3-dimensional Arrangements
132. Explanation (Answer; a)
Due to uniform and long-range forces, crystalline solids show sharp melting point.
133. Which of the following is NOT CORRECT for ionic crystals?
(a)They possess high melting point and boiling point
(b)All are electrolytes
(c)Exhibit the property of isomorphism
(d)Exhibit directional properties of the bond
133. Explanation (Answer; d)
Ionic bond is non-directional.
134. Which one of the following is incorrect statement regarding sublime solids?
(a) They directly pass into gaseous state on heating.
(b) Camphor, NH4Cl and naphthalene are few examples of sublime solids.
(c) The reason for direct conversion to gaseous state is that they have hydrogen bonding.
(d) In sublime solids, the intermolecular forces are much less than ordinary solids.
134.Explanation (Answer; c)
Sublime solids have unusually weaker intermolecular forces than ordinary solids.
135. Isomorphous substances have:
(a) Same physical and chemical properties.
(b) Same physical but different chemical properties.
(c) Different physical but same chemical properties.
(d) Different physical and chemical properties
135.Explanation (Answer; d)
Already explained in previous MCQs.
136.Which one of the following is not a property of crystalline solids?
(a) They have definite shape because their particles are arranged in an orderly three dimensional network.
(b) They have sharp melting point.
(c) They have cleavage plane.
(d) They are isotropic.
136.Explanation (Answer; d)
crystalline solids are anisotropic.
137. Which of the following is correct?
(a) NaF and MgO are isomorphous having cubic structure.
(b) NaNO3 and CaCO3 are isomorphous having trigonal crystal.
(c) ZnSO4 and NiSO4 are isomorphous having orthorhombic crystal.
(d) All of the above.
137. Explanation (Answer; d)
All given options contain isomorphous crystal pairs.
138. Which one of the following is incorrect statement regarding atomic solids?
(a) They consist of non-metallic atoms packed and held together by metallic bond.
(b) They have metallic luster on their surface.
(c) They are malleable and ductile.
(d) They are conductors of heat and electricity.
138.Explanation (Answer; a)
Atomic solids consist of metal atoms.
139. Which one of the following is incorrect statement regarding electrovalent solids?
(a) They consist of molecules held together by electrostatic force of attraction.
(b) They have high melting points.
(c) They are malleable and ductile having high tensile strength.
(d) They do not conduct electricity in solid state.
139.Explanation (Answer; c)
Metallic solids are malleable and ductile. Ionic solids are brittle.
140. Which of the following statements is TRUE?
(a) Both crystalline and amorphous solids are isotropic
(b) Both crystalline and amorphous solids are anisotropic
(c) Crystalline solids are always isotropic and amorphous solids are anisotropic
(d) Crystalline solids are anisotropic and amorphous solids are isotropic
140.Explanation (Answer; d)
Crystalline solids are anisotropic and amorphous solids are isotropic.
141. For the various types of interactions, the CORRECT order of increasing strength is:
(a) covalent < hydrogen bonding < van der Waal’s < dipole-dipole
(b) van der Waal’s < hydrogen bonding < dipole-dipole < covalent
(c) van der Waal’s < hydrogen bonding < dipole-dipole < covalent
(d) van der Waal’s < dipole-dipole < hydrogen bonding < covalent
141.Explanation (Answer; d)
van der Waal’s < dipole-dipole < hydrogen bonding < covalent
142.Which one of the following is incorrect statement regarding crystalline solids?
(a) They have regular repeating three dimensional structures of constituent particles.
(b) They have sharp melting point.
(c) They have symmetry.
(d) They are not true solids.
142.Explanation (Answer; d)
Crystalline solids true solids.
143. The structure of ionic solids depends upon the property of the cations and anions which is
(a) Size
(b) Attraction
(c) Radius ratio
(d) Charge density
143.Explanation (Answer; c)
The structure of ionic solids depends upon the radius ratio of cation and anion.
144. Coordination number of Na+ ion in NaCl is 6 and that of cesium ion in CsCl is 8.This is because:
(a) I.P of Cs is less than Na
(b) size of Na+ is less than Cs+
(c) attraction of Na+ is higher than Cs+
(d) None of the above
144.Explanation (Answer; b)
NaCl and CsCl have similar formula. However, they have different structures.
The radius ratio of NaCl lies in the range of 0.414-0.732. Hence, it has a coordination number of 6, which is the octahedral arrangement. On the other hand, the radius ratio of CsCl lies in the range of 0.732-1.0. Hence, it has a coordination number of 8. that is, it has a body-centered cubic arrangement.
The difference in the ranges of radius ratio in NaCl and CsCl is because of the fact that the size of Na+ is less than the Cs+.
145. Which of the following pairs is not isomorphous?
(a) BaSO4, KMnO4
(b) KClO4, KBF4
(c) FeSO4.7H2O, MgSO4.7H2O
(d) NaClO3, NaNO3
145.Explanation (Answer; d)
Isomorphous structures are those that have the same crystal shape.
Here, the shape as predicted by VSEPR theory of:
ClO3−→ Pyramidal
NO3− → Planar.
Hence, NaClO3 and NaNO3 are not isomorphous.
146. Which of the following exists as covalent crystals in the solid state?
(a) Sulphur
(b) Iodine
(c) Silicon
(d) Phosphorus
146.Explanation (Answer; c)
Silicon forms covalent crystals.
147. Which of the following is true about the value of refractive index of quartz glass?
(a) Different in different directions
(b) Same in all directions
(c) cannot be measured
(d) always zero
147.Explanation (Answer; b)
Quartz is a mineral with the chemical formula SiO2, and like almost all minerals, it is a crystalline solid.
Quartz glass is an amorphous solid because it is formed by fusing the crystal and then cooling it rapidly.
Being an amorphous solid, quartz glass is isotropic having same magnitude of physical properties in all directions.
148. Which of the following is an amorphous solid ?
(a) Graphite (C)
(b) Quartz glass (SiO2)
(c) Chrome alum
(d) Silicon carbide (SiC)
148.Explanation (Answer; b)
Quartz glass (SiO2) is an amorphous solid due to its short range order of constituent particles.
Note Quartz is a crystalline solid while quartz glass is an amorphous solid.
149. When molten form of crystalline solid is rapidly cooled, it changes into :
(a) Liquid crystals
(b) amorphous solid
(c) insulator
(d) super conductor
149.Explanation (Answer; b)
When a molten form of crystalline solid is cooled rapidly, the particles do not get enough time to make on ordered arrangement due to quenching of material. Hence the structure becomes unordered and non-repetitive changing into amorphous form.
150. Which of the following substance does not sublime?
(a) Ammonium chloride
(b) Dry ice
(c) Sodium chloride
(d) Iodine
141.Explanation (Answer; c)
Sodium Chloride is an ionic solid and has high melting and boiling points. So it can not change in vapour phase simply at atmospheric pressure hence it cannot sublime.
Ammonium chloride, dry ice and iodine undergo sublimation which on heating without coming in the liquid state directly convert in a gaseous state.
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