Crystalline solids MCQs With Answer provide B. Pharm students a focused way to master solid-state chemistry relevant to pharmaceutics. This introduction covers key concepts like unit cell, Bravais lattices, packing efficiency, Miller indices, X-ray diffraction (PXRD), polymorphism, hydrates/solvates, crystal defects, and their impact on drug stability, solubility, and dissolution. Emphasis on analytical techniques (DSC, Scherrer equation, Rietveld) and crystallization principles helps bridge theory with formulation challenges. These keyword-rich MCQs strengthen understanding of crystalline behavior, solid-state characterization, and formulation strategies essential for drug development. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What defines a crystalline solid?
- A material with atoms arranged in a regular, repeating three-dimensional pattern
- A solid with only amorphous regions and no long-range order
- A substance that melts over a broad temperature range
- A polymer with randomly coiled chains
Correct Answer: A material with atoms arranged in a regular, repeating three-dimensional pattern
Q2. What is a unit cell in crystallography?
- The smallest repeating structural unit that completely describes the crystal lattice
- The macroscopic crystal habit visible under a microscope
- A defect site where an atom is missing
- A measurement of crystal hardness
Correct Answer: The smallest repeating structural unit that completely describes the crystal lattice
Q3. How many Bravais lattices exist in three dimensions?
- 7
- 14
- 24
- 32
Correct Answer: 14
Q4. Which of the following is a characteristic of a primitive (P) unit cell?
- Contains lattice points only at the corners
- Has lattice points at corners and face centers
- Always represents the most compact packing
- Is only found in cubic crystals
Correct Answer: Contains lattice points only at the corners
Q5. What is the coordination number of atoms in a face-centered cubic (fcc) structure?
- 6
- 8
- 12
- 4
Correct Answer: 12
Q6. Which structure has a packing efficiency of approximately 74%?
- Simple cubic
- Body-centered cubic
- Face-centered cubic (ccp)
- Diamond cubic
Correct Answer: Face-centered cubic (ccp)
Q7. What do Miller indices (hkl) represent?
- The orientation of crystallographic planes relative to the unit cell axes
- The chemical composition of the unit cell
- The fracture toughness of a crystal
- The number of defects per unit volume
Correct Answer: The orientation of crystallographic planes relative to the unit cell axes
Q8. How are Miller indices determined for a plane that intercepts axes at a, b/2, and ∞?
- (1, 2, 0)
- (1, 0.5, ∞)
- (2, 1, 0)
- (1, 1, 1)
Correct Answer: (2, 1, 0)
Q9. What is Bragg’s law for X-ray diffraction?
- nλ = 2d sin θ
- E = hν
- ρ = m/V
- λ = hc/E
Correct Answer: nλ = 2d sin θ
Q10. Why is powder X-ray diffraction (PXRD) essential in pharmaceutical solids analysis?
- It identifies crystalline phases, polymorphs, and degree of crystallinity
- It measures only the particle size distribution
- It provides direct chemical assay of impurities
- It images internal microstructure like SEM
Correct Answer: It identifies crystalline phases, polymorphs, and degree of crystallinity
Q11. Which equation (name) is used to estimate crystallite size from XRD peak broadening?
- Van’t Hoff equation
- Scherrer equation
- Henderson–Hasselbalch equation
- Arrhenius equation
Correct Answer: Scherrer equation
Q12. Peak broadening in PXRD can be caused by which factors?
- Small crystallite size and microstrain
- Only instrument misalignment
- High purity and large crystals
- Absence of defects
Correct Answer: Small crystallite size and microstrain
Q13. What is polymorphism in pharmaceutical solids?
- The ability of a molecule to exist in more than one crystalline form
- The conversion of a crystal into an amorphous solid
- The formation of co-crystals only
- The hydration of a crystal by water molecules
Correct Answer: The ability of a molecule to exist in more than one crystalline form
Q14. Which polymorph is typically more soluble and often less stable?
- Thermodynamically stable polymorph
- Metastable polymorph
- Hydrated polymorph
- Covalent network polymorph
Correct Answer: Metastable polymorph
Q15. What distinguishes a hydrate from a solvate?
- Hydrate contains water molecules; solvate contains any solvent molecules
- Hydrate has stronger ionic bonds than solvates
- Hydrate is amorphous while solvate is crystalline
- Hydrate always decreases solubility, solvates increase it
Correct Answer: Hydrate contains water molecules; solvate contains any solvent molecules
Q16. How does crystallinity generally affect drug dissolution?
- Higher crystallinity usually decreases dissolution rate
- Higher crystallinity always increases dissolution rate
- Crystallinity has no effect on dissolution
- Only particle size matters, not crystallinity
Correct Answer: Higher crystallinity usually decreases dissolution rate
Q17. Which analytical technique is most used to detect polymorphic transitions by measuring heat flow?
- FTIR spectroscopy
- Differential scanning calorimetry (DSC)
- Gas chromatography
- UV-Vis spectroscopy
Correct Answer: Differential scanning calorimetry (DSC)
Q18. What is a point defect in a crystal?
- A localized imperfection such as a vacancy or interstitial
- A planar defect like a grain boundary
- A long-range dislocation line
- A surface imperfection only
Correct Answer: A localized imperfection such as a vacancy or interstitial
Q19. Which defect type involves a missing cation-anion pair in an ionic crystal?
- Frenkel defect
- Schottky defect
- Edge dislocation
- Screw dislocation
Correct Answer: Schottky defect
Q20. In a Frenkel defect, which process occurs?
- Atom vacates its lattice site and occupies an interstitial site
- Equal numbers of cations and anions are missing
- Vacancies form only at the surface
- Planar faults develop between grains
Correct Answer: Atom vacates its lattice site and occupies an interstitial site
Q21. What is the coordination number in the NaCl structure for each ion?
- 4
- 6
- 8
- 12
Correct Answer: 6
Q22. The CsCl structure differs from NaCl primarily by which feature?
- CsCl has coordination number 8 with a simple cubic arrangement for chloride
- CsCl is amorphous
- CsCl has a molecular crystal lattice
- CsCl contains water of crystallization always
Correct Answer: CsCl has coordination number 8 with a simple cubic arrangement for chloride
Q23. Which stacking sequence corresponds to hexagonal close packing (hcp)?
- ABCABC
- ABAB
- AABBCC
- ABCA
Correct Answer: ABAB
Q24. Which technique can provide quantitative phase analysis and unit cell parameters from powder diffraction data?
- Rietveld refinement
- Karl Fischer titration
- Optical microscopy
- Gel permeation chromatography
Correct Answer: Rietveld refinement
Q25. How is density (ρ) of a crystalline solid calculated from unit cell data?
- ρ = Z·M / (N_A·V_cell)
- ρ = M / Z
- ρ = V_cell / (Z·M)
- ρ = N_A / (Z·M·V_cell)
Correct Answer: ρ = Z·M / (N_A·V_cell)
Q26. What does Z represent in unit cell calculations?
- The number of formula units per unit cell
- The atomic number of the element
- The coordination number
- The unit cell edge length
Correct Answer: The number of formula units per unit cell
Q27. Which type of solid is characterized by directional covalent bonds and very high melting points (e.g., diamond, SiO2 network)?
- Molecular solids
- Ionic solids
- Covalent network solids
- Metallic solids
Correct Answer: Covalent network solids
Q28. How do crystal defects generally influence chemical reactivity and solubility?
- Defects increase surface energy and can increase solubility and reactivity
- Defects make crystals chemically inert
- Defects always decrease solubility
- Defects have no measurable effect on reactivity
Correct Answer: Defects increase surface energy and can increase solubility and reactivity
Q29. In crystallization, what distinguishes nucleation from crystal growth?
- Nucleation is formation of stable nuclei; growth is enlargement of those nuclei
- Nucleation requires solvents; growth occurs in vacuum only
- Nucleation happens only at low temperature; growth only at high temperature
- They are the same process with different names
Correct Answer: Nucleation is formation of stable nuclei; growth is enlargement of those nuclei
Q30. What is Ostwald’s rule of stages relevant to crystallization?
- The most stable phase always forms first
- The kinetically favored, less stable phase often forms first and may transform to a more stable phase
- Polymorphs never interconvert
- Hydrates form only after anhydrate forms
Correct Answer: The kinetically favored, less stable phase often forms first and may transform to a more stable phase
Q31. Which of the following best describes anisotropy in crystalline solids?
- Physical properties vary with crystallographic direction
- All physical properties are identical in every direction
- Optical properties are absent in crystals
- Anisotropy applies only to liquids
Correct Answer: Physical properties vary with crystallographic direction
Q32. What role does hydrogen bonding play in drug crystal packing?
- It stabilizes specific packing motifs and influences polymorphism and solubility
- It always destabilizes crystal structures
- It is irrelevant in organic molecular crystals
- It only affects metallic crystals
Correct Answer: It stabilizes specific packing motifs and influences polymorphism and solubility
Q33. Which technique complements PXRD to estimate degree of crystallinity by measuring melting enthalpy?
- Differential scanning calorimetry (DSC)
- Mass spectrometry
- Size-exclusion chromatography
- Atomic absorption spectroscopy
Correct Answer: Differential scanning calorimetry (DSC)
Q34. Which phenomenon describes the transformation of a solvated crystal into a different anhydrous form upon solvent loss?
- Desolvation or dehydration leading to polymorphic change
- Schottky defect formation
- Frenkel migration
- Thermal expansion without structural change
Correct Answer: Desolvation or dehydration leading to polymorphic change
Q35. What is the primary reason metastable polymorphs can be more bioavailable?
- They have higher lattice energy than stable forms
- They often possess higher solubility and faster dissolution rates
- They are always less soluble by definition
- They convert immediately to amorphous form in water
Correct Answer: They often possess higher solubility and faster dissolution rates
Q36. Which of the following is an example of a planar defect?
- Grain boundary
- Vacancy
- Edge dislocation
- Interstitial atom
Correct Answer: Grain boundary
Q37. How does temperature generally affect vacancy concentration in a crystal?
- Vacancy concentration decreases with increasing temperature
- Vacancy concentration increases with increasing temperature
- Temperature has no effect on vacancies
- Vacancies only form at absolute zero
Correct Answer: Vacancy concentration increases with increasing temperature
Q38. Which property is commonly used to distinguish crystalline from amorphous solids?
- Sharp, well-defined peaks in X-ray diffraction for crystalline solids
- Both show identical PXRD patterns
- Amorphous solids have multiple Bragg peaks
- Crystalline solids never melt
Correct Answer: Sharp, well-defined peaks in X-ray diffraction for crystalline solids
Q39. What is the reciprocal lattice used for in crystallography?
- To describe diffraction conditions and relate plane spacings to scattering vectors
- To calculate molecular weight from unit cell
- To measure particle size directly
- To model chemical reactivity of defects
Correct Answer: To describe diffraction conditions and relate plane spacings to scattering vectors
Q40. In powder diffraction indexing, what does a higher 2θ angle generally indicate about the corresponding d-spacing?
- The d-spacing is larger for higher 2θ
- The d-spacing is smaller for higher 2θ
- 2θ and d-spacing are unrelated
- d-spacing equals 2θ numerically
Correct Answer: The d-spacing is smaller for higher 2θ
Q41. Which crystallization additive is used to control crystal habit and morphology?
- Habit modifier or growth inhibitor
- Only pH buffers
- Only strong acids
- Nonpolar solvents only
Correct Answer: Habit modifier or growth inhibitor
Q42. What is the Scherrer equation dependent parameter that must be corrected for instrument broadening?
- Scattering factor
- Peak width (full width at half maximum, FWHM)
- Unit cell volume
- Molar mass
Correct Answer: Peak width (full width at half maximum, FWHM)
Q43. Which solid type typically has metallic bonding and delocalized electrons?
- Ionic solids
- Metallic solids
- Molecular solids
- Covalent network solids
Correct Answer: Metallic solids
Q44. How does pressure influence polymorphism in pharmaceutical solids?
- Pressure can stabilize denser polymorphs and induce phase transitions
- Pressure only affects amorphous solids
- Polymorph stability is independent of pressure
- Pressure always converts crystals to liquids
Correct Answer: Pressure can stabilize denser polymorphs and induce phase transitions
Q45. Which method is most suitable to detect very small populations of crystalline impurity in a bulk powder?
- Optical microscopy only
- High-resolution powder X-ray diffraction and careful peak analysis
- Simple melting point determination
- pH measurement
Correct Answer: High-resolution powder X-ray diffraction and careful peak analysis
Q46. What is the primary practical significance of polymorphism in drug development?
- Polymorphism has no commercial impact
- Different polymorphs can have different solubility, stability, and patentability implications
- All polymorphs are chemically identical and interchangeable without study
- Polymorphism only affects color, not performance
Correct Answer: Different polymorphs can have different solubility, stability, and patentability implications
Q47. What is the main difference between single-crystal XRD and powder XRD?
- Single-crystal XRD provides detailed atomic positions and bond geometry; powder XRD gives phase identification and unit cell parameters
- Powder XRD gives atomic positions; single-crystal only phases
- They are identical techniques with different names
- Single-crystal XRD cannot determine crystal symmetry
Correct Answer: Single-crystal XRD provides detailed atomic positions and bond geometry; powder XRD gives phase identification and unit cell parameters
Q48. Which of the following best describes cleavage in crystals?
- Tendency to break along specific crystallographic planes where bonding is weakest
- Random fracture with no preferred direction
- Formation of voids within the crystal lattice
- Recrystallization into a different polymorph
Correct Answer: Tendency to break along specific crystallographic planes where bonding is weakest
Q49. What is the effect of microparticulate crystalline defects on powder compaction and tableting?
- Defects can alter plasticity, compaction behavior, and mechanical strength of tablets
- Defects only influence color and taste
- Defects make powders impossible to compress
- There is no measurable effect on tablet properties
Correct Answer: Defects can alter plasticity, compaction behavior, and mechanical strength of tablets
Q50. Which pair contrasts vacancy and interstitial point defects?
- Vacancy: missing atom; Interstitial: extra atom in void space
- Vacancy: extra atom; Interstitial: missing atom
- Both are planar defects
- Neither affects diffusion properties
Correct Answer: Vacancy: missing atom; Interstitial: extra atom in void space
