Objectives of size separation MCQs With Answer

Introduction: Understanding the objectives of size separation MCQs with answer is essential for B. Pharm students focusing on particle size distribution, sieving, and classification techniques. This introduction covers why particle size control matters in formulation, dissolution, flow properties, content uniformity, and stability testing. Key topics include sieving methods, wet and dry separation, PSD parameters (D10, D50, D90), efficiency, and regulatory considerations for quality control. Targeted practice with MCQs helps consolidate knowledge, interpret PSD data, select appropriate separation methods, and troubleshoot laboratory issues. This guide is designed to boost exam readiness and practical skills in pharmaceutical size separation. ‘Now let’s test your knowledge with 50 MCQs on this topic.’

Q1. What is the primary objective of size separation in pharmaceutical powder processing?

• To change chemical composition of drug particles
• To obtain a desired particle size distribution for consistent product performance
• To sterilize the powder
• To add moisture to powders

Correct Answer: To obtain a desired particle size distribution for consistent product performance

Q2. Which parameter describes the particle diameter at which 50% of the sample by mass is finer?

• D10
• D90
• D50 (median)
• Span

Correct Answer: D50 (median)

Q3. Which technique is most appropriate for separating coarse granules from fines using a stack of woven meshes?

• Air classification
• Sieving
• Centrifugation
• Filtration

Correct Answer: Sieving

Q4. What does a high span value indicate about a particle size distribution?

• Very narrow size distribution
• Broad size distribution
• All particles are the same size
• Particles are spherical

Correct Answer: Broad size distribution

Q5. Which of the following is NOT an objective of size separation in formulation development?

• Improve dissolution rate
• Enhance flow properties
• Change the drug’s intrinsic solubility
• Ensure content uniformity

Correct Answer: Change the drug’s intrinsic solubility

Q6. In wet sieving, why is liquid used during size separation?

• To dissolve all particles
• To reduce agglomeration and improve passage of fine particles
• To increase static electricity
• To make particles heavier

Correct Answer: To reduce agglomeration and improve passage of fine particles

Q7. Which instrument provides detailed particle size distribution by measuring light scattering?

• Vibratory sieve shaker
• Laser diffraction analyzer
• Optical comparator
• Rotary tablet press

Correct Answer: Laser diffraction analyzer

Q8. Which factor most affects sieving efficiency?

• Tablet color
• Mesh aperture size and particle shape
• Time of day
• Operator’s height

Correct Answer: Mesh aperture size and particle shape

Q9. What is the typical unit for reporting sieve mesh aperture in pharmaceutical sieving?

• Mol/L
• Micrometers (µm)
• Percent w/v
• Kilograms

Correct Answer: Micrometers (µm)

Q10. Air classification separates particles primarily based on which property?

• Electrical conductivity
• Hydrophobicity
• Particle aerodynamic diameter (size and density)
• Magnetic susceptibility

Correct Answer: Particle aerodynamic diameter (size and density)

Q11. Which PSD parameter indicates the smallest size below which 10% of the sample lies?

• D10
• D50
• D90
• Mode

Correct Answer: D10

Q12. Why is particle size control important for inhalation formulations?

• It determines taste
• It influences deposition in the respiratory tract and bioavailability
• It controls tablet shape
• It regulates dissolution in stomach only

Correct Answer: It influences deposition in the respiratory tract and bioavailability

Q13. Which separation method is most suitable for very fine particles (<10 µm) prone to agglomeration?

• Manual sieving
• Wet classification or ultrasonic sieving
• Coarse mesh sieving
• Gravity settling only

Correct Answer: Wet classification or ultrasonic sieving

Q14. What is the main advantage of using laser diffraction for PSD analysis?

• Low accuracy for all sizes
• Rapid measurement over a wide size range with good reproducibility
• Measures chemical impurities
• Requires no sample preparation regardless of material

Correct Answer: Rapid measurement over a wide size range with good reproducibility

Q15. Which of the following affects particle separation by sedimentation?

• Particle density and fluid viscosity
• Tablet coating color
• Ambient noise
• Operator’s mood

Correct Answer: Particle density and fluid viscosity

Q16. In a sieve analysis, what is the reason for using a stack of sieves in descending aperture sizes?

• To mix the sample thoroughly
• To fractionate particles into successive size ranges for PSD determination
• To increase sample temperature
• To sterilize each fraction

Correct Answer: To fractionate particles into successive size ranges for PSD determination

Q17. Which is the correct interpretation if D90 is 200 µm for a batch?

• 90% of particles are larger than 200 µm
• 90% of particles are finer than 200 µm
• Median size is 200 µm
• Only 10% of particles are 200 µm

Correct Answer: 90% of particles are finer than 200 µm

Q18. Which regulatory consideration is related to particle size in pharmaceuticals?

• Particle size has no regulatory relevance
• Particle size can be a critical quality attribute (CQA) affecting safety and efficacy
• Only color must be controlled
• Regulators prohibit sieving

Correct Answer: Particle size can be a critical quality attribute (CQA) affecting safety and efficacy

Q19. What is the effect of reducing particle size on dissolution rate according to the Noyes–Whitney equation?

• Decreases dissolution rate by lowering surface area
• Increases dissolution rate by increasing surface area
• Has no effect
• Makes the drug insoluble

Correct Answer: Increases dissolution rate by increasing surface area

Q20. Which factor can cause blinding of sieve mesh during sieving?

• Particles much smaller than mesh apertures
• Sticky or electrostatically charged particles and moist samples
• High ambient humidity only
• Using too many sieves

Correct Answer: Sticky or electrostatically charged particles and moist samples

Q21. What is ultrasonic sieving primarily used for?

• Heating samples
• Enhancing passage of fine, cohesive particles through mesh by vibration at ultrasonic frequency
• Measuring chemical composition
• Drying the sample

Correct Answer: Enhancing passage of fine, cohesive particles through mesh by vibration at ultrasonic frequency

Q22. Which statement is true about particle shape in size separation?

• Shape does not influence sieving or flow
• Irregular shapes can hinder passage through sieves and reduce flowability
• Only spherical particles are tested
• Shape only affects color

Correct Answer: Irregular shapes can hinder passage through sieves and reduce flowability

Q23. Which measurement gives information about spread of the PSD (polydispersity)?

• D50 only
• Span or standard deviation of the distribution
• Color index
• Tablet hardness

Correct Answer: Span or standard deviation of the distribution

Q24. For granulation operations, why is controlling upper particle size important?

• To avoid segregation and ensure uniform filling and compaction
• To change the API potency
• To increase moisture content
• To change taste

Correct Answer: To avoid segregation and ensure uniform filling and compaction

Q25. Which separation technique is based on centrifugal force to separate particles by size/density?

• Vibratory sieving
• Centrifugation/centrifugal classification
• Magnetic separation
• Manual hand sorting

Correct Answer: Centrifugation/centrifugal classification

Q26. When performing sieve analysis, what is the purpose of tapping or shaking the sieve stack?

• To alter chemical composition
• To aid particle passage through apertures and reduce bridging
• To cool the sample
• To sterilize the sieves

Correct Answer: To aid particle passage through apertures and reduce bridging

Q27. Which phenomenon makes fine particles adhere to sieve mesh and reduce separation efficiency?

• Van der Waals forces and electrostatic attraction
• Gravity only
• Color difference
• Thermal convection

Correct Answer: Van der Waals forces and electrostatic attraction

Q28. Which of the following is a critical quality attribute assessed by size separation in topical suspensions?

• Flavor profile
• Viscosity and particle settling rate/stability
• Tablet disintegration time
• Capsule shell thickness

Correct Answer: Viscosity and particle settling rate/stability

Q29. Which unit operation commonly precedes sieving to break down agglomerates in powders?

• Coating
• Milling or comminution
• Packaging
• Lyophilization

Correct Answer: Milling or comminution

Q30. What is the likely effect on flowability if the particle size distribution becomes narrower and particles are more spherical?

• Flowability decreases dramatically
• Flowability generally improves
• No change
• Material becomes sticky

Correct Answer: Flowability generally improves

Q31. Which method is suitable for continuous industrial-scale size separation of powders by density and size using air flow?

• Batch sieving
• Air classifier
• Manual screening
• Paper filtration

Correct Answer: Air classifier

Q32. In PSD reporting, what does cumulative percent finer plot show?

• Percentage of particles larger than a given size
• Percentage of particles finer than a given size across the size range
• Chemical impurities vs size
• Storage conditions

Correct Answer: Percentage of particles finer than a given size across the size range

Q33. Which pre-treatment can improve sieve analysis results for hygroscopic powders?

• Adding solvents
• Drying to specified moisture content
• Heating beyond decomposition temperature
• Adding acid

Correct Answer: Drying to specified moisture content

Q34. Which of the following is a limitation of wet sieving?

• Cannot separate very fine cohesive powders
• Risk of dissolving or altering materials sensitive to the liquid medium
• Always faster than dry sieving
• Does not reduce agglomeration

Correct Answer: Risk of dissolving or altering materials sensitive to the liquid medium

Q35. What is a common corrective action if sieve blinding occurs during analysis?

• Increase sample moisture
• Use ultrasonic cleaning, change mesh size, or use anti-static measures
• Ignore results
• Paint the sieve

Correct Answer: Use ultrasonic cleaning, change mesh size, or use anti-static measures

Q36. Why is sample size important in sieve analysis?

• Sample size has no impact on results
• Insufficient or excessive sample size can bias PSD results due to stacking or overloading
• Larger samples always give worse results
• Only color matters

Correct Answer: Insufficient or excessive sample size can bias PSD results due to stacking or overloading

Q37. Which PSD technique provides morphological (shape) information in addition to size?

• Laser diffraction only
• Optical image analysis or dynamic image analysis
• Standard sieve analysis only
• Viscometry

Correct Answer: Optical image analysis or dynamic image analysis

Q38. Which statement best summarizes the role of size separation in bioavailability of poorly soluble drugs?

• Size separation always reduces bioavailability
• Reducing particle size can enhance dissolution and potentially improve bioavailability of poorly soluble drugs
• Only temperature affects bioavailability
• Particle size is unrelated to dissolution

Correct Answer: Reducing particle size can enhance dissolution and potentially improve bioavailability of poorly soluble drugs

Q39. What is the effect of cohesive forces on powder sieving and handling?

• Cohesion improves sieving efficiency
• Cohesive forces cause agglomeration, reducing sieving efficiency and flowability
• Cohesion only affects color
• Cohesion makes powders magnetic

Correct Answer: Cohesive forces cause agglomeration, reducing sieving efficiency and flowability

Q40. Which control parameter should be validated for a sieve shaker used in QC testing?

• Vibration amplitude/frequency and test time
• Operator’s favorite music
• Room color
• Sample flavor

Correct Answer: Vibration amplitude/frequency and test time

Q41. For a suspension, why is particle size distribution critical to stability?

• Smaller particles always sediment faster
• PSD affects sedimentation rate, redispersibility, and visual appearance; wider PSD may lead to caking
• Only viscosity matters
• PSD controls chemical degradation only

Correct Answer: PSD affects sedimentation rate, redispersibility, and visual appearance; wider PSD may lead to caking

Q42. Which technique separates particles by allowing smaller ones to pass through a porous medium while retaining larger ones?

• Sieving/screening
• Electrophoresis
• X-ray diffraction
• Lyophilization

Correct Answer: Sieving/screening

Q43. What is a common QC acceptance criterion related to particle size for tablet granules?

• All granules must be 1 mm exactly
• Specified percent by weight must fall within defined sieve ranges to ensure uniform filling and compaction
• Only the API content matters
• Color matching is sufficient

Correct Answer: Specified percent by weight must fall within defined sieve ranges to ensure uniform filling and compaction

Q44. Which property is NOT directly determined by particle size?

• Surface area
• Dissolution rate
• Intrinsic chemical structure
• Flowability

Correct Answer: Intrinsic chemical structure

Q45. Which corrective measure can reduce static charging and improve sieving of fine powders?

• Increase humidity, use antistatic agents or grounding
• Freeze the powder
• Paint the sieve
• Remove all vibration

Correct Answer: Increase humidity, use antistatic agents or grounding

Q46. During particle size analysis by laser diffraction, which assumption may introduce error?

• Particles are transparent
• Assuming particles are spherical when they are irregular
• Laser light is monochromatic
• Detector is calibrated

Correct Answer: Assuming particles are spherical when they are irregular

Q47. Which analytical value would indicate a formulation has an excess of fines that may cause dusting and segregation?

• Low D10 value with high percent below a small size threshold
• High D90 only
• Zero percent fines
• Perfectly uniform particles

Correct Answer: Low D10 value with high percent below a small size threshold

Q48. For nanoparticle formulations, what specialized separation or characterization methods are commonly used?

• Standard hand sieves
• Ultracentrifugation, dynamic light scattering (DLS), and electron microscopy
• Tablet hardness tester
• Colorimeter only

Correct Answer: Ultracentrifugation, dynamic light scattering (DLS), and electron microscopy

Q49. How does particle density influence settling velocity in a suspension?

• Higher particle density generally increases settling velocity according to Stoke’s law (if spherical and laminar conditions apply)
• Density has no effect
• Lower density always increases settling
• Only particle color matters

Correct Answer: Higher particle density generally increases settling velocity according to Stoke’s law (if spherical and laminar conditions apply)

Q50. Which practice helps ensure representative sampling for PSD analysis?

• Taking a single small scoop from the top of a lot
• Using randomized, stratified samples and proper sample splitting to account for heterogeneity
• Only sampling after sieving
• Sampling only the largest particles

Correct Answer: Using randomized, stratified samples and proper sample splitting to account for heterogeneity

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