The Solid State — Class 12 Chemistry

1. The smallest repeating structural unit of a crystal which when repeated in space generates the entire lattice is called:

1. Bravais lattice
2. Unit cell ✅
3. Basis
4. Crystal system

2. The number of Bravais lattices in three dimensions is:

1. 7
2. 14 ✅
3. 23
4. 3

3. Packing efficiency of face centred cubic (fcc) structure is approximately:

1. 52%
2. 74% ✅
3. 68%
4. 100%

4. In a simple cubic unit cell, number of atoms per cell is:

1. 2
2. 1 ✅
3. 4
4. 8

5. Coordination number of atoms in a bcc lattice is:

1. 4
2. 8 ✅
3. 6
4. 12

6. Which of the following is NOT a crystalline solid?

1. Diamond
2. Graphite
3. Glass ✅
4. Rock salt

7. A Frenkel defect is characterized by:

1. Equal number of cation and anion vacancies
2. Cation displaced to interstitial position leaving a vacancy ✅
3. Loss of lattice water only
4. Substitutional impurity

8. Schottky defect is typically found in ionic solids where ions are:

1. Replaced by other ions
2. Missing from lattice as pair of vacancies (both cation and anion vacancies) ✅
3. At interstitial sites only
4. All occupied perfectly

9. Bragg's law nλ = 2d sinθ is used in:

1. Calculating density of ionic solids
2. X-ray diffraction for crystal structure determination ✅
3. Calculating packing efficiency
4. Balancing redox reactions

10. In close packed structures, the coordination number of atoms at octahedral void is:

1. 4
2. 6
3. 6 ✅
4. 8

11. The number of tetrahedral voids in a close packed structure is:

1. Equal to number of atoms ✅
2. Twice the number of atoms
3. Half the number of atoms
4. Zero

12. Packing efficiency of bcc structure is approximately:

1. 52%
2. 68% ✅
3. 74%
4. 100%

13. A substance showing metallic bonding will typically exhibit:

1. Low electrical conductivity
2. High electrical conductivity and malleability ✅
3. High solubility in water
4. Non-lustrous appearance

14. The formula unit of rock salt structure (NaCl) has coordination number of:

1. 4
2. 6 ✅
3. 8
4. 12

15. Ionic solids are generally:

1. Conductors in solid state
2. Insulators in solid state but conduct in molten state ✅
3. Good conductors at room temperature
4. Always magnetic

16. An extrinsic semiconductor is made by:

1. Pure silicon at low temperature
2. Doping intrinsic semiconductor with impurity atoms ✅
3. Compressing metal crystal
4. Applying a magnetic field

17. Which defect increases ionic conductivity in ionic solids?

1. Dislocation density
2. Schottky defect (vacancies allowing ion movement) ✅
3. Perfect lattice
4. Grain growth only

18. In NaCl structure, the unit cell is best described as:

1. Simple cubic of Na with Cl at body centers
2. Face-centered cubic lattice of Cl- with Na+ in octahedral holes ✅
3. Body-centered cubic of Na and Cl mixed
4. Hexagonal close packing of both ions

19. Band gap of a semiconductor is typically:

1. Greater than 5 eV
2. Small, around 1 eV (varies, e.g., Si ~1.1 eV) ✅
3. Zero always
4. Infinite

20. In a unit cell, atoms touching along face diagonal is characteristic of:

1. Simple cubic
2. Face-centered cubic (fcc) ✅
3. Body-centered cubic (bcc)
4. Hexagonal close-packed only

21. The radius ratio rule helps predict:

1. Color of ionic crystals
2. Coordination number and structure of ionic solids ✅
3. Melting point precisely
4. Electrical conductivity only

22. Which solid has a network covalent structure leading to very high melting point?

1. NaCl
2. Diamond (network covalent) ✅
3. Ar (argon)
4. H2O

23. The presence of dislocations in metals is responsible for:

1. Electrical insulation
2. Plastic deformation and ductility ✅
3. Perfect brittleness
4. Zero thermal conductivity

24. Which solid among the following will show ionic bonding?

1. C diamond
2. NaCl ✅
3. Si
4. Au (metallic)

25. Coordination number of octahedral void is:

1. 4
2. 6 ✅
3. 8
4. 12

26. In X-ray diffraction, higher θ angles correspond to:

1. Larger interplanar spacing d
2. Smaller interplanar spacing d (since sinθ increases with θ) ✅
3. No change in d
4. Infinite d

27. The density of a crystalline solid can be calculated using unit cell parameters and:

1. Molecular weight and Avogadro's number ✅
2. Only melting point
3. Only ionic charges
4. Only band gap

28. Which solid exhibits both covalent and metallic characteristics in bonding?

1. Diamond
2. Graphite (covalent layers with delocalized electrons) ✅
3. NaCl
4. Ar

29. Which of the following increases with temperature in intrinsic semiconductors?

1. Band gap energy
2. Number of charge carriers (electrons & holes) ✅
3. Resistivity drastically increases
4. All carriers vanish

30. In a ccp (fcc) arrangement, fraction of tetrahedral holes occupied if one out of every 2 atoms occupies tetrahedral site is:

1. All of them
2. 50% ✅ (since number of tetrahedral holes equals number of atoms)
3. 25%
4. 0%

31. A material with overlapping valence and conduction bands behaves as:

1. Insulator
2. Conductor (metal) ✅
3. Semiconductor
4. Dielectric only

32. Which defect involves replacement of a lattice ion by a foreign ion?

1. Vacancy defect
2. Substitutional defect ✅
3. Interstitial defect
4. Frenkel defect

33. Ionic solids are brittle because:

1. They are ductile
2. Like-charged ions align on stress causing repulsion and fracture ✅
3. They have metallic bonding
4. They are amorphous

34. The number of atoms per unit cell in fcc structure is:

1. 1
2. 4 ✅
3. 2
4. 8

35. Which solid has delocalized electrons responsible for metallic luster?

1. Diamond
2. Metallic solids (e.g., Cu, Au) ✅
3. Ionic solids
4. Molecular solids

36. In a close-packed structure, octahedral voids are larger than tetrahedral voids. True or False?

1. False
2. True ✅
3. Depends on element only
4. Never

37. Which technique gives direct information about atomic arrangement in crystals?

1. IR spectroscopy
2. X-ray diffraction ✅
3. Mass spectrometry
4. UV-Vis spectroscopy

38. The presence of vacancy defects will:

1. Increase density
2. Decrease density ✅
3. Have no effect on density
4. Always make material magnetic

39. In semiconductors, doping with pentavalent impurity results in:

1. p-type semiconductor
2. n-type semiconductor (extra electrons) ✅
3. Increase band gap greatly
4. Insulating behavior

40. Which is true for amorphous solids compared to crystalline solids?

1. They have long-range order
2. They lack long-range order and have isotropic properties ✅
3. They show sharp melting points
4. They have periodic lattice

41. The defect where atoms of different size replace host atoms is called:

1. Frenkel defect
2. Substitutional defect ✅
3. Schottky defect
4. Interstitialcy

42. Which of the following structures has coordination number 12?

1. Simple cubic
2. Close-packed structures (fcc/hcp) ✅
3. BCC
4. NaCl

43. A material with a band gap of 0 eV is classified as:

1. Insulator
2. Conductor/metal ✅
3. Semiconductor
4. Dielectric

44. The number of octahedral voids in a close packed structure equals:

1. Twice the number of atoms
2. Equal to the number of atoms ✅
3. Half the number of atoms
4. Zero

45. Which of the following increases ionic mobility in solid electrolytes?

1. Decreasing temperature
2. Creating defects and doping to provide vacancies ✅
3. Perfect crystalline order
4. Removing impurities

46. Which solid is an example of a molecular solid?

1. NaCl
2. Ice (solid H2O) ✅
3. Diamond
4. Metallic copper

47. The formula for theoretical density (ρ) involves Avogadro's number (N_A), mass of atoms in unit cell (m), and:

1. Lattice energy only
2. Volume of unit cell ✅
3. Band gap energy
4. Coordination number only

48. The main difference between ccp and hcp arrangements is:

1. Type of atoms only
2. Layer stacking sequence (ABC... vs ABAB...) ✅
3. Coordination number differs drastically
4. Packing efficiency is zero for one

49. Which of these solids conducts electricity in molten state but not in solid state?

1. Metals
2. Graphite
3. Ionic solids (e.g., NaCl) ✅
4. Diamond