Particle shape MCQs With Answer

Particle shape MCQs With Answer

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Particle shape MCQs With Answer

Particle shape and morphology are central to pharmaceutics, influencing powder flow, packing, compaction, dissolution, aerosolization and content uniformity in B. Pharm formulations. Understanding descriptors like sphericity, aspect ratio, Feret diameter, circularity and convexity helps predict behavior during milling, granulation, tableting and inhalation product development. Techniques such as optical microscopy, SEM, dynamic image analysis and micro-CT quantify shape and surface roughness, guiding formulation and process optimization. Mastery of particle-shape principles aids rational selection of unit operations and excipients for robust drug products. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which term best describes the geometric outline and surface features of a particle that influence its behavior in powders?

  • Particle shape or morphology
  • Particle density
  • Crystalline lattice energy
  • Polymorphic form

Correct Answer: Particle shape or morphology

Q2. Which analytical technique provides direct high-resolution visualization of particle surface shape and fine morphology?

  • Scanning electron microscopy (SEM)
  • Laser diffraction
  • Gas pycnometry
  • X-ray diffraction (XRD)

Correct Answer: Scanning electron microscopy (SEM)

Q3. Aspect ratio as a particle-shape descriptor is defined as:

  • Ratio of particle length to width
  • Particle surface area divided by volume
  • Ratio of equivalent spherical diameter to actual diameter
  • Particle density divided by porosity

Correct Answer: Ratio of particle length to width

Q4. Equivalent spherical diameter (ESD) is useful because it:

  • Allows comparison of non-spherical particles to spheres by volume or surface area
  • Directly measures particle surface roughness
  • Is independent of particle density
  • Is obtained only from SEM images

Correct Answer: Allows comparison of non-spherical particles to spheres by volume or surface area

Q5. Elongated or needle-like particles typically affect powder flow by causing:

  • Decreased flowability and increased interlocking
  • Improved flowability due to rolling
  • No change in flow behavior
  • Lower compressibility leading to harder tablets

Correct Answer: Decreased flowability and increased interlocking

Q6. Which shape descriptor is commonly used to express how close a particle is to a perfect sphere (value between 0 and 1)?

  • Sphericity
  • Feret diameter
  • Convexity
  • Porosity

Correct Answer: Sphericity

Q7. Which of the following is NOT a particle shape descriptor used in image analysis?

  • Color hue
  • Circularity
  • Aspect ratio
  • Solidity (convexity-related)

Correct Answer: Color hue

Q8. Dynamic image analysis (automated image capture of flowing particles) provides which of the following?

  • High-throughput size and shape distributions for non-spherical particles
  • True three-dimensional internal structure like micro-CT
  • Direct measurement of aerodynamic diameter without calculations
  • Only particle color information

Correct Answer: High-throughput size and shape distributions for non-spherical particles

Q9. How does increased particle surface area due to irregular shape generally affect dissolution rate of poorly soluble drugs?

  • It increases dissolution rate by providing more wetted surface
  • It decreases dissolution rate uniformly
  • It has no effect on dissolution
  • It only affects dissolution for gases

Correct Answer: It increases dissolution rate by providing more wetted surface

Q10. The aerodynamic diameter is defined as the diameter of a unit-density sphere that has the same:

  • Settling velocity in air as the particle
  • Geometric Feret diameter
  • Surface roughness as the particle
  • Mass median diameter in water

Correct Answer: Settling velocity in air as the particle

Q11. Which technique can provide true 3D internal and external particle morphology useful for porosity and shape analysis?

  • X-ray micro-computed tomography (micro-CT)
  • Laser diffraction
  • Atomic absorption spectroscopy
  • Optical density measurement

Correct Answer: X-ray micro-computed tomography (micro-CT)

Q12. Crystalline drug particles often appear as which type of shapes under microscopy?

  • Faceted, angular crystals due to lattice habit
  • Perfectly spherical regardless of process
  • Always fibrous and amorphous
  • Invisible under SEM

Correct Answer: Faceted, angular crystals due to lattice habit

Q13. Spray-drying commonly produces particles with what typical morphology?

  • Spherical hollow or solid particles
  • Large faceted crystals
  • Needle-like elongated crystals
  • Flat platelets

Correct Answer: Spherical hollow or solid particles

Q14. Circularity (a common image-analysis metric) is mathematically expressed as which of the following?

  • 4π × (area) / (perimeter)^2
  • Perimeter / area
  • Aspect ratio × convexity
  • Volume / surface area

Correct Answer: 4π × (area) / (perimeter)^2

Q15. The numerical value of sphericity typically ranges between which limits?

  • 0 (very non-spherical) to 1 (perfect sphere)
  • -1 to +1
  • 10 to 100
  • It is unbounded

Correct Answer: 0 (very non-spherical) to 1 (perfect sphere)

Q16. How does particle shape influence powder bulk density and packing?

  • Irregular or elongated shapes often reduce packing efficiency and lower bulk density
  • All shapes pack identically under any condition
  • Spheres always produce the lowest bulk density
  • Shape only affects chemical stability, not packing

Correct Answer: Irregular or elongated shapes often reduce packing efficiency and lower bulk density

Q17. Which unit operation is most likely to dramatically change particle shape from angular to more rounded?

  • Milling/grinding
  • Lyophilization
  • Recrystallization without agitation
  • Thin-film coating

Correct Answer: Milling/grinding

Q18. Which technique is most suitable for quantifying nanoscale surface roughness on individual particles?

  • Atomic force microscopy (AFM)
  • Laser diffraction
  • Optical microscopy at low magnification
  • Gas chromatography

Correct Answer: Atomic force microscopy (AFM)

Q19. Irregular particle shapes can worsen content uniformity in blends primarily by increasing:

  • Particle segregation during handling
  • Chemical degradation
  • Thermal stability
  • Solution pH

Correct Answer: Particle segregation during handling

Q20. For inhalation aerosols, which measurement is most relevant to predict lung deposition considering particle shape and density?

  • Aerodynamic diameter
  • Optical color
  • True geometric diameter only
  • Melting point

Correct Answer: Aerodynamic diameter

Q21. Feret diameter refers to:

  • The distance between two parallel tangents of a particle measured in a given direction
  • The diameter of the largest inscribed circle
  • Equivalent spherical diameter based on volume
  • Particle electrical charge

Correct Answer: The distance between two parallel tangents of a particle measured in a given direction

Q22. Which statement about laser diffraction and particle shape is TRUE?

  • Laser diffraction estimates size distributions but provides limited direct shape information
  • Laser diffraction directly yields convexity and circularity values
  • Laser diffraction measures internal porosity accurately
  • Laser diffraction gives 3D shape reconstructions

Correct Answer: Laser diffraction estimates size distributions but provides limited direct shape information

Q23. Convexity or solidity in image analysis compares particle area to:

  • Area of its convex hull
  • Perimeter squared
  • Equivalent spherical volume
  • Mass divided by density

Correct Answer: Area of its convex hull

Q24. Which particle habit modifier strategy is commonly used during crystallization to control particle shape?

  • Addition of specific surfactants or additives that adsorb onto crystal faces
  • Increasing ambient humidity only after crystallization
  • Using high-energy milling post-crystallization without seeding
  • Freezing the solvent to form amorphous shapes

Correct Answer: Addition of specific surfactants or additives that adsorb onto crystal faces

Q25. Plate-like or flaky particles influence tableting behavior by:

  • Often producing weaker compacts at equivalent pressure due to poor particle interlocking
  • Always enhancing tablet hardness compared to spherical particles
  • Eliminating the need for binders
  • Reducing powder bulk volume to zero

Correct Answer: Often producing weaker compacts at equivalent pressure due to poor particle interlocking

Q26. Image analysis can quantify external particle shape but typically cannot directly measure which property?

  • Internal porosity and connected pore networks
  • Projected area and perimeter
  • Aspect ratio from 2D projection
  • Feret diameters in two axes

Correct Answer: Internal porosity and connected pore networks

Q27. Which statement is FALSE regarding laser diffraction for particle characterization?

  • Laser diffraction accurately determines detailed particle shape descriptors like circularity
  • It provides rapid volume-based size distributions
  • It assumes spherical particles when converting scattering to size
  • It can be used over a wide size range with appropriate optics

Correct Answer: Laser diffraction accurately determines detailed particle shape descriptors like circularity

Q28. An ellipsoid particle is characterized by:

  • Three principal semi-axes of different lengths
  • Only a single diameter like a sphere
  • Zero surface area
  • Identical behavior to cubes in packing

Correct Answer: Three principal semi-axes of different lengths

Q29. Why are habit modifiers used during crystallization in pharmaceutical processing?

  • To alter crystal face growth rates and produce more desirable particle shapes for processing
  • To change the chemical identity of the API
  • To sterilize the batch
  • To increase melting point irreversibly

Correct Answer: To alter crystal face growth rates and produce more desirable particle shapes for processing

Q30. Which practical approach is most appropriate to reduce needle-like crystals and obtain more equant crystals for better flow?

  • Use specific crystallization solvents and habit modifiers or seeded crystallization to change habit
  • Increase storage temperature to above melting point
  • Freeze-dry the needle crystals without solvent change
  • Rely solely on tablet coating to mask poor flow

Correct Answer: Use specific crystallization solvents and habit modifiers or seeded crystallization to change habit

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