Particle size determination methods MCQs With Answer

Introduction

Particle size determination methods MCQs With Answer are essential for B. Pharm students studying pharmaceutics, formulation development, and quality control. Understanding particle size analysis, granulometry, and particle size distribution (PSD) helps predict dissolution, bioavailability, stability, and flow properties. Key techniques include sieving, laser diffraction, dynamic light scattering (DLS), sedimentation methods, microscopy, and Coulter counter analysis. Familiarity with concepts like D10/D50/D90, span, polydispersity index, Stokes’ law, and sample dispersion is vital for selecting appropriate methods for powders, suspensions, aerosols, and nanoparticles. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which technique measures particle size based on light scattering and provides volume-based particle size distribution?

• Sieving
• Laser diffraction
• Optical microscopy
• Coulter counter

Correct Answer: Laser diffraction

Q2. Which particle size parameter represents the median diameter where 50% of the sample by volume (or number) is smaller?

• D10
• D50
• D90
• Span

Correct Answer: D50

Q3. Which method uses Stokes’ law and sedimentation velocity to determine particle size?

• Dynamic light scattering (DLS)
• Laser diffraction
• Sedimentation (e.g., centrifuge or settling tube)
• Electron microscopy

Correct Answer: Sedimentation (e.g., centrifuge or settling tube)

Q4. Which technique is most appropriate for measuring submicron particles (1–1000 nm) in colloidal suspensions?

• Sieving
• Laser diffraction
• Dynamic light scattering (DLS)
• Air jet sieving

Correct Answer: Dynamic light scattering (DLS)

Q5. The Coulter counter determines particle size by measuring:

• Light scattering intensity
• Electrical impedance change as particles pass through an aperture
• Mass of individual particles
• Charge distribution on particle surfaces

Correct Answer: Electrical impedance change as particles pass through an aperture

Q6. Which parameter describes the width of the particle size distribution and is calculated as (D90–D10)/D50?

• Polydispersity index
• Span
• Mean diameter
• Specific surface area

Correct Answer: Span

Q7. In laser diffraction, an assumption that affects results is that particles are:

• Perfectly spherical
• Electrically neutral
• Charged
• Magnetic

Correct Answer: Perfectly spherical

Q8. Which microscopy technique provides the highest resolution for direct particle imaging and size measurement?

• Optical microscopy
• Scanning electron microscopy (SEM)
• Light scattering
• Sieving

Correct Answer: Scanning electron microscopy (SEM)

Q9. For powders intended for inhalation (aerosols), which size range is most critical for deposition in the deep lung?

• > 10 µm
• 2–5 µm
• 50–100 µm
• 100–1000 µm

Correct Answer: 2–5 µm

Q10. Dynamic light scattering reports an intensity-weighted hydrodynamic diameter; this can bias results toward:

• Smallest particles
• Largest particles or aggregates
• Only spherical particles
• Only charged particles

Correct Answer: Largest particles or aggregates

Q11. Which sample preparation step is crucial before measuring particle size in suspensions to avoid aggregation artifacts?

• Drying the sample completely
• Proper dispersion using sonication or surfactant
• Heating to 100°C
• Adding electrolytes to induce flocculation

Correct Answer: Proper dispersion using sonication or surfactant

Q12. Which technique directly measures specific surface area and can be related to average particle size for spherical particles?

• B.E.T. gas adsorption
• Laser diffraction
• Optical microscopy
• Coulter counter

Correct Answer: B.E.T. gas adsorption

Q13. Which limitation is common to sieve analysis for particle size determination?

• Cannot analyze particles > 1 mm
• Unsuitable for very fine powders below ~38 µm
• Requires vacuum conditions
• Gives only number-weighted distribution

Correct Answer: Unsuitable for very fine powders below ~38 µm

Q14. In the context of particle sizing, D90 means:

• 90% of particles are larger than this diameter
• 90% of particles are smaller than this diameter
• Diameter of the largest particle
• Average diameter of all particles

Correct Answer: 90% of particles are smaller than this diameter

Q15. Which method provides particle-by-particle sizing and concentration information for dilute suspensions?

• Laser diffraction
• Dynamic light scattering
• Nanoparticle tracking analysis (NTA) or Coulter counter
• Sieving

Correct Answer: Nanoparticle tracking analysis (NTA) or Coulter counter

Q16. Which factor does NOT directly affect sedimentation rate according to Stokes’ law?

• Particle radius
• Density difference between particle and fluid
• Viscosity of fluid
• Color of the particle

Correct Answer: Color of the particle

Q17. Polydispersity index (PDI) from DLS indicates:

• Particle color distribution
• Uniformity of particle sizes in suspension
• Electrical charge distribution
• Mass of particles

Correct Answer: Uniformity of particle sizes in suspension

Q18. Which particle sizing method is least affected by particle refractive index assumptions?

• Laser diffraction
• Dynamic light scattering
• Sieving
• Optical microscopy with calibrated scale

Correct Answer: Sieving

Q19. When reporting particle size for regulatory filings, best practice includes providing:

• Only a single number without method details
• Method used, sample prep, distribution metrics (e.g., D10/D50/D90) and instrument settings
• Only the instrument brand
• Only electron micrographs

Correct Answer: Method used, sample prep, distribution metrics (e.g., D10/D50/D90) and instrument settings

Q20. Which technique can distinguish particle shape and morphology visually while also allowing size measurement?

• Laser diffraction
• Scanning or transmission electron microscopy (SEM/TEM)
• Coulter counter
• Air permeability testing

Correct Answer: Scanning or transmission electron microscopy (SEM/TEM)

Q21. Which method is most suitable for routine QC of coarse powders in bulk pharmaceutical manufacturing?

• Dynamic light scattering
• Sieving
• Nano tracking analysis
• Atomic force microscopy

Correct Answer: Sieving

Q22. Aggregation in a sample prior to measurement typically causes measured particle size to be:

• Smaller than true primary particle size
• Larger than true primary particle size
• Unchanged
• Reported as zero

Correct Answer: Larger than true primary particle size

Q23. Which instrument detects scattered light intensity fluctuations over time to determine particle diffusion and derive size?

• Laser diffraction
• Dynamic light scattering (photon correlation spectroscopy)
• Sieving
• Optical balance

Correct Answer: Dynamic light scattering (photon correlation spectroscopy)

Q24. For non-spherical particles, which statement is correct regarding size reporting?

• Reported diameter always equals true longest dimension
• Equivalent spherical diameter is typically reported and depends on measurement principle
• Size cannot be measured
• All methods give identical sizes

Correct Answer: Equivalent spherical diameter is typically reported and depends on measurement principle

Q25. Which parameter derived from PSD indicates the fraction of fine particles likely to pass through an inhaler and deposit in lungs?

• Mass median aerodynamic diameter (MMAD)
• Specific surface area
• Bulk density
• Melting point

Correct Answer: Mass median aerodynamic diameter (MMAD)

Q26. In laser diffraction, forward scattering correlates mainly with:

• Small particles (<1 µm)
• Large particles (>1 µm)
• Chemical composition
• Electrical charge

Correct Answer: Large particles (>1 µm)

Q27. Which sample characteristic must be controlled to obtain reproducible DLS measurements?

• Sample turbidity and concentration
• Color of the vial
• Ambient radioactivity
• Magnetic field strength

Correct Answer: Sample turbidity and concentration

Q28. Which technique provides rapid, bulk particle sizing and is commonly used for excipient and active pharmaceutical ingredient (API) powders during formulation?

• Gas adsorption BET only
• Laser diffraction
• Transmission electron microscopy only
• Thermogravimetric analysis

Correct Answer: Laser diffraction

Q29. When converting surface area from BET to an equivalent particle diameter for spherical, non-porous particles, what additional property is required?

• Particle color
• True density of the material
• Electrical conductivity
• Viscosity of the dispersant

Correct Answer: True density of the material

Q30. Which statement best describes the influence of refractive index on optical particle sizing methods?

• Refractive index is irrelevant for all optical methods
• Accurate knowledge of particle and dispersant refractive indices improves conversion of scattering patterns to size
• Only electrical methods require refractive index
• Refractive index only affects sieving

Correct Answer: Accurate knowledge of particle and dispersant refractive indices improves conversion of scattering patterns to size

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com