Particle size and shape MCQs With Answer

Particle size and shape MCQs With Answer is an essential topic for B. Pharm students focused on how particle size, particle shape, and particle size distribution influence drug formulation, stability, dissolution rate, powder flow, and bioavailability. Understanding granulometry techniques (sieving, laser diffraction, microscopy), specific surface area (BET), aerodynamic diameter, and concepts like agglomeration, aggregation, and Ostwald ripening is critical for rational dosage form design. This keyword-rich introduction links theory to practical measurements—Stokes’ law, D10/D50/D90 metrics, zeta potential, and Carr’s index—helping students interpret data and optimize formulations. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which parameter best describes the particle size at which 50% of the sample by volume is smaller?

• Number mean diameter
• Mode diameter
• Median diameter (D50)
• Geometric standard deviation

Correct Answer: Median diameter (D50)

Q2. Which technique directly measures particle shape and surface morphology at high magnification?

• Laser diffraction
• Scanning electron microscopy (SEM)
• Sieving
• Photon correlation spectroscopy

Correct Answer: Scanning electron microscopy (SEM)

Q3. According to Stokes’ law, sedimentation velocity of a spherical particle in a fluid is proportional to which term?

• Particle radius
• Square of particle radius
• Cube of particle radius
• Inverse of particle radius

Correct Answer: Square of particle radius

Q4. Which measurement reports the spread of particle sizes and is often calculated as (D90−D10)/D50?

• Span
• Polydispersity index
• Specific surface area
• Bulk porosity

Correct Answer: Span

Q5. Which method is most suitable for measuring very small nanoparticles (1–100 nm) in suspension?

• Optical microscopy
• Laser diffraction
• Dynamic light scattering (DLS)
• Sieve analysis

Correct Answer: Dynamic light scattering (DLS)

Q6. BET analysis is used to determine which property important for dissolution and reactivity?

• Particle density
• Specific surface area
• Bulk volume
• Pore volume only

Correct Answer: Specific surface area

Q7. Aerodynamic diameter accounts for which factors to predict particle behavior in air?

• Only geometric diameter
• Geometric diameter and particle density
• Only particle shape
• Only surface charge

Correct Answer: Geometric diameter and particle density

Q8. Which process describes growth of larger particles at the expense of smaller ones in a dispersion?

• Sintering
• Ostwald ripening
• Aggregation due to van der Waals
• Mechanical attrition

Correct Answer: Ostwald ripening

Q9. Which parameter is most directly increased when particle size is reduced for a drug substance?

• Melting point
• Specific surface area
• Bulk density
• Particle zeta potential

Correct Answer: Specific surface area

Q10. In powder flow assessment, a high Carr’s compressibility index indicates what?

• Excellent flowability
• Poor flowability and likely compressibility issues
• Low moisture content
• Uniform particle shape

Correct Answer: Poor flowability and likely compressibility issues

Q11. Which technique provides a volume-based particle size distribution by measuring light scattering angle?

• Dynamic light scattering
• Laser diffraction
• Transmission electron microscopy
• Tap density measurement

Correct Answer: Laser diffraction

Q12. What effect does acicular (needle-like) particle shape typically have on powder behavior?

• Improves flow and reduces interlocking
• Increases inter-particle friction and poor flow
• Makes packing denser and improves compressibility
• Eliminates electrostatic charges

Correct Answer: Increases inter-particle friction and poor flow

Q13. Which descriptor refers to tightly bonded primary particles forming one solid mass?

• Agglomerate
• Aggregate
• Sediment
• Suspension

Correct Answer: Aggregate

Q14. Polydispersity Index (PDI) in DLS indicates what about a sample?

• The chemical composition of particles
• The uniformity or width of particle size distribution
• The absolute particle density
• The porosity of particles

Correct Answer: The uniformity or width of particle size distribution

Q15. Which of the following milling methods is widely used for micronization without heat generation?

• Ball milling
• Jet milling (air jet mill)
• Hot melt milling
• Cryo-precipitation

Correct Answer: Jet milling (air jet mill)

Q16. D10, D50 and D90 are percentiles that describe which aspect of particle size distribution?

• Particle shape anisotropy
• Percentiles representing sizes below which 10%, 50%, 90% of the sample lie
• Surface charge distribution
• Moisture content distribution

Correct Answer: Percentiles representing sizes below which 10%, 50%, 90% of the sample lie

Q17. Which factor most strongly increases dissolution rate according to the Noyes–Whitney equation?

• Decreasing surface area
• Increasing diffusion layer thickness
• Increasing surface area by particle size reduction
• Decreasing saturation solubility

Correct Answer: Increasing surface area by particle size reduction

Q18. Which property is commonly measured by tap density and bulk density tests?

• Particle chemical stability
• Flowability and packing characteristics of powders
• Surface functionality
• True particle density

Correct Answer: Flowability and packing characteristics of powders

Q19. Which microscopy technique gives internal structure and crystallinity information at atomic resolution?

• Scanning electron microscopy (SEM)
• Optical microscopy
• Transmission electron microscopy (TEM)
• Laser diffraction

Correct Answer: Transmission electron microscopy (TEM)

Q20. High zeta potential magnitude (positive or negative) generally indicates what about particle dispersions?

• Increased tendency to aggregate
• Enhanced electrostatic stabilization and reduced aggregation
• Higher sedimentation rate due to mass increase
• Lower specific surface area

Correct Answer: Enhanced electrostatic stabilization and reduced aggregation

Q21. Which statement about aerodynamic diameter is true for inhalation therapy?

• Geometric diameter alone determines lung deposition
• Particles with aerodynamic diameter ~1–5 µm deposit in the lower respiratory tract
• Aerodynamic diameter is irrelevant for aerosols
• Only particle electrical charge affects deposition

Correct Answer: Particles with aerodynamic diameter ~1–5 µm deposit in the lower respiratory tract

Q22. In sieve analysis, which factor primarily affects separation efficiency?

• Color of powder
• Sieve aperture size and particle shape
• Ambient humidity only
• Particle surface chemistry exclusively

Correct Answer: Sieve aperture size and particle shape

Q23. Which intervention can reduce aggregation of hydrophobic drug nanoparticles in suspension?

• Adding a surfactant or stabilizer
• Increasing particle concentration only
• Raising temperature to dissolve particles
• Removing all solvents

Correct Answer: Adding a surfactant or stabilizer

Q24. The term “specific surface area” is expressed in which units?

• g/cm3
• m2/g
• µm
• particles per mL

Correct Answer: m2/g

Q25. Which distribution plot shows cumulative percentage versus particle size?

• Frequency histogram
• Cumulative distribution curve
• Phase diagram
• Zeta potential plot

Correct Answer: Cumulative distribution curve

Q26. How does particle irregularity (non-sphericity) typically influence packing density?

• Irregular particles pack more efficiently than spheres
• Non-spherical particles usually reduce packing density and increase voids
• Shape has no effect on packing
• Irregularity always increases true density

Correct Answer: Non-spherical particles usually reduce packing density and increase voids

Q27. Which parameter is derived from powder flow testing and relates tapped to bulk density?

• Angle of repose
• Hausner ratio
• Polydispersity index
• Ostwald coefficient

Correct Answer: Hausner ratio

Q28. Which process is most likely when very fine particles stick together due to high surface energy?

• Granulation
• Aggregation or agglomeration
• Fractionation
• Lyophilization

Correct Answer: Aggregation or agglomeration

Q29. Which analytical method distinguishes between primary particle size and agglomerate size in dry powders?

• Mercury intrusion porosimetry only
• Electron microscopy combined with image analysis
• Bulk density measurement only
• UV–Vis spectroscopy

Correct Answer: Electron microscopy combined with image analysis

Q30. What is a common pharmaceutical consequence of reducing particle size to the nanoscale?

• Decreased saturation solubility
• Increased dissolution rate and often increased apparent solubility
• Guaranteed improved chemical stability
• Reduced surface area

Correct Answer: Increased dissolution rate and often increased apparent solubility

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