Introduction: Size reduction is a core topic in pharmaceutics that explores how particle size, milling methods, and process parameters influence drug formulation and performance. This concise guide on “Factors affecting size reduction MCQs With Answer” helps B. Pharm students grasp critical concepts such as material hardness, brittleness, moisture content, mill type, grinding media, speed, screen size, and energy input. Understanding these factors is essential for optimizing milling efficiency, preventing contamination, controlling heat-sensitive APIs, and improving dissolution and bioavailability. Each question links theoretical principles to practical pharmaceutical scenarios, reinforcing learning and exam readiness. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which material property most directly determines the energy required for size reduction?
- Colour of the material
- Hardness
- Bulk density
- Odour
Correct Answer: Hardness
Q2. Which law relates energy required for size reduction to change in particle size and is most appropriate for fine grinding?
- Kick’s law
- Rittinger’s law
- Archimedes’ principle
- Boyle’s law
Correct Answer: Rittinger’s law
Q3. Moisture content in feed material commonly affects which outcome during milling?
- Colour spectrum
- Agglomeration and caking
- Electrical conductivity
- Optical rotation
Correct Answer: Agglomeration and caking
Q4. Which milling method is most suitable for producing micronized APIs without contamination from metal wear?
- Hammer milling with steel hammers
- Ball milling with steel balls
- Jet milling using high-velocity gas
- Stone grinding
Correct Answer: Jet milling using high-velocity gas
Q5. The term ‘comminution’ refers to:
- Mixing powders uniformly
- Reducing particle size by mechanical means
- Drying powders under vacuum
- Coating particles with polymers
Correct Answer: Reducing particle size by mechanical means
Q6. Which factor of a grinding mill directly affects the shear and impact forces on particles?
- Ambient room colour
- Rotational speed
- Manufacturer logo
- Packaging type
Correct Answer: Rotational speed
Q7. For brittle pharmaceutical solids, which mechanism predominantly causes breakage?
- Plastic deformation
- Cohesive sintering
- Crack propagation and fragmentation
- Swelling
Correct Answer: Crack propagation and fragmentation
Q8. Which particle characteristic most influences dissolution rate after size reduction?
- Particle colour
- Surface area to volume ratio
- Container label
- Bottle cap size
Correct Answer: Surface area to volume ratio
Q9. In ball milling, decreasing grinding media size generally leads to:
- Lower specific surface area
- Higher fines production and finer particles
- Increased macroparticle formation
- Complete elimination of heat generation
Correct Answer: Higher fines production and finer particles
Q10. Which measurement technique is commonly used for submicron particle size analysis in pharmaceutics?
- Sieving with 1 mm mesh
- Laser diffraction and dynamic light scattering
- Visual inspection only
- Thermogravimetric analysis
Correct Answer: Laser diffraction and dynamic light scattering
Q11. High feed rate into a mill typically causes:
- Increased residence time
- Reduced breakage efficiency and coarser product
- Improved fines generation
- Lower mill power consumption per tonne
Correct Answer: Reduced breakage efficiency and coarser product
Q12. Which factor increases risk of thermal degradation during milling of heat-sensitive APIs?
- Using cryogenic cooling
- High mill speed and prolonged milling time
- Wet milling with chilled media
- Working under inert atmosphere
Correct Answer: High mill speed and prolonged milling time
Q13. Bond’s law is most applicable for estimating energy requirements in which size range?
- Very coarse crushing only
- Intermediate grinding and conventional industrial mills
- Nanoparticle formation exclusively
- Only for liquids
Correct Answer: Intermediate grinding and conventional industrial mills
Q14. Which mill type uses centrifugal forces with grinding media for wet or dry milling in pharma labs?
- Roller compactor
- Planetary ball mill
- Rotary tablet press
- Fluid bed dryer
Correct Answer: Planetary ball mill
Q15. Which feed property promotes ductile deformation rather than brittle fracture during grinding?
- High brittleness
- High ductility and plasticity
- High porosity
- Low thermal conductivity
Correct Answer: High ductility and plasticity
Q16. Which operational parameter controls maximum particle size that exits a mill with a screen?
- Ambient humidity only
- Screen or sieve aperture size
- Colour of the screen
- Operator’s manual
Correct Answer: Screen or sieve aperture size
Q17. Cryogenic milling is especially useful for:
- Reducing energy consumption by heating feed
- Processing heat-sensitive, elastic, or sticky materials by embrittlement
- Increasing moisture content
- Enhancing oxidation reactions
Correct Answer: Processing heat-sensitive, elastic, or sticky materials by embrittlement
Q18. Which is a common sign of contamination during size reduction in metal mills?
- Loss of particle size distribution
- Detection of trace metal by ICP or visual metallic specks
- Reduced humidity
- Improved flowability
Correct Answer: Detection of trace metal by ICP or visual metallic specks
Q19. In wet milling, what advantage is provided compared to dry milling for pharmaceuticals?
- Higher risk of oxidation
- Reduced heat generation and better dispersion of particles
- Impossible to control particle size
- Always increases contamination
Correct Answer: Reduced heat generation and better dispersion of particles
Q20. Which factor most influences scale-up from laboratory mill to production mill?
- Colour of lab equipment
- Geometric similarity, energy input per unit mass, and residence time
- Operator’s height
- Day of the week
Correct Answer: Geometric similarity, energy input per unit mass, and residence time
Q21. Agglomeration during milling is often caused by:
- Excessive drying
- Surface forces, moisture, and electrostatic attractions
- Using non-stick liners only
- Reducing feed concentration
Correct Answer: Surface forces, moisture, and electrostatic attractions
Q22. Specific surface area increases when particle size:
- Increases
- Decreases
- Remains unchanged
- Depends only on colour
Correct Answer: Decreases
Q23. Which instrument measures particle size distribution by light scattering?
- Fourier-transform infrared spectrometer
- Laser diffraction particle size analyzer
- pH meter
- Analytical balance
Correct Answer: Laser diffraction particle size analyzer
Q24. Which grinding mechanism is dominant in a hammer mill?
- Compression only
- Impact and shear
- Evaporation
- Biochemical degradation
Correct Answer: Impact and shear
Q25. Which factor affects the degree of fines generation in a mill?
- Feed colour
- Feed hardness, mill speed, and residence time
- Packaging design
- Cleaning schedule only
Correct Answer: Feed hardness, mill speed, and residence time
Q26. Which condition reduces electrostatic charging during dry milling?
- Low humidity and low grounding
- Increasing humidity and proper grounding or antistatic measures
- Using highly insulating liners only
- Maximizing friction intentionally
Correct Answer: Increasing humidity and proper grounding or antistatic measures
Q27. The Bond work index is used to estimate:
- Thermal stability of API
- Specific energy consumption for size reduction
- Colour stability
- Viscosity of a liquid
Correct Answer: Specific energy consumption for size reduction
Q28. Which factor increases contamination risk when milling pharmaceuticals?
- Using ceramic or pharmaceutical grade liners
- Using worn metal liners and grinding media
- Operating under inert gas
- Regular maintenance
Correct Answer: Using worn metal liners and grinding media
Q29. For sticky or cohesive powders, which milling approach is often preferred?
- High-speed dry impact milling without cooling
- Wet milling or cryogenic milling to reduce stickiness
- Not milling at all because cohesion cannot be overcome
- Monetary incentives
Correct Answer: Wet milling or cryogenic milling to reduce stickiness
Q30. Which particle attribute is most relevant to powder flow after size reduction?
- Particle shape and size distribution
- Color of powder
- Brand of mill used
- Ambient music in lab
Correct Answer: Particle shape and size distribution
Q31. Which grinding mill is widely used for nanoparticle milling in industry and research?
- Roller compactor
- High-pressure jet mill
- Sieve shaker
- Tablet press
Correct Answer: High-pressure jet mill
Q32. Which sample preparation step is critical before particle size measurement by laser diffraction?
- Ensuring monodisperse suspension without agglomerates
- Removing all solvents permanently
- Heating sample to 200°C
- Coating with metal
Correct Answer: Ensuring monodisperse suspension without agglomerates
Q33. Which phenomenon increases when particles are very fine and surface forces dominate?
- Gravitational settling
- Cohesive interparticle forces and powder caking
- Magnetic alignment
- Colour fading
Correct Answer: Cohesive interparticle forces and powder caking
Q34. Which operational change reduces heat generation in a ball mill?
- Increasing milling duration dramatically
- Intermittent operation or using cooling medium
- Using smaller grinding media without cooling
- Sealing the mill to trap heat
Correct Answer: Intermittent operation or using cooling medium
Q35. Which parameter describes the fraction of feed reporting to a particular sieve size?
- Bulk density
- Particle size distribution or cumulative undersize
- Viscosity
- Melting point
Correct Answer: Particle size distribution or cumulative undersize
Q36. Which mill is least likely to be used for wet milling in pharma?
- Colloid mill
- Bead mill
- Fluid energy (jet) mill
- High-shear wet mill
Correct Answer: Fluid energy (jet) mill
Q37. What is the main advantage of micronization of an API?
- Reduced bioavailability
- Improved dissolution rate and potential bioavailability
- Increased taste masking only
- Eliminates need for quality control
Correct Answer: Improved dissolution rate and potential bioavailability
Q38. Which factor affects both energy consumption and wear in mills?
- Operating under vacuum
- Grinding media material and hardness
- Colour of grinding media
- Ambient lighting
Correct Answer: Grinding media material and hardness
Q39. Which breakage function describes probability of breakage as a function of particle size?
- Selection function S(x)
- Breakage distribution function b(x,y)
- Arrhenius constant
- Partition coefficient
Correct Answer: Selection function S(x)
Q40. In milling, what effect does increased porosity of feed particles have?
- Always increases hardness
- May reduce fracture strength and alter breakage mechanisms
- Has no effect on grindability
- Makes particles magnetically active
Correct Answer: May reduce fracture strength and alter breakage mechanisms
Q41. Which approach helps minimize cross-contamination between batches during milling?
- Using the same uncleaned mill for all products
- Dedicated equipment, thorough cleaning, or validated cleaning procedures
- Skipping cleaning if visual inspection is clean
- Using powdered detergent in the mill
Correct Answer: Dedicated equipment, thorough cleaning, or validated cleaning procedures
Q42. Which property is measured by sieve analysis?
- Particle size distribution by discrete size fractions
- Chemical purity
- Thermal decomposition
- Optical activity
Correct Answer: Particle size distribution by discrete size fractions
Q43. Which phenomenon can reduce mill throughput during wet milling?
- Effective dispersion of particles
- Excessive viscosity and slurry thickening
- Using low solid concentration
- Optimised bead loading
Correct Answer: Excessive viscosity and slurry thickening
Q44. Which mill parameter adjustment can reduce generation of ultrafines (nanosized dust) in a production run?
- Increase mill energy input continuously
- Reduce mill speed or adjust residence time and use coarser media
- Increase feed moisture to 100%
- Remove classifying screens
Correct Answer: Reduce mill speed or adjust residence time and use coarser media
Q45. Breakage mechanisms include impact, compression, attrition and:
- Evaporation
- Abrasion
- Photosynthesis
- Diffusion only
Correct Answer: Abrasion
Q46. Which factor is critical when selecting a mill for sterile pharmaceutical production?
- Colour of the product
- Ability to sterilize or operate aseptically and ease of cleaning
- Location of the supplier
- Size of company logo
Correct Answer: Ability to sterilize or operate aseptically and ease of cleaning
Q47. Which technique reduces particle size by precipitation rather than mechanical grinding?
- Jet milling
- Anti-solvent precipitation / controlled crystallization
- Hammer milling
- Roller crushing
Correct Answer: Anti-solvent precipitation / controlled crystallization
Q48. Which particle characteristic measured by microscopy helps understand fragmentation patterns?
- Chemical composition only
- Particle shape and aspect ratio
- Viscosity of surrounding medium
- Thermal conductivity
Correct Answer: Particle shape and aspect ratio
Q49. Which consideration is most important to protect a hygroscopic API during size reduction?
- Expose to ambient humid air
- Control humidity, use inert atmosphere or dry gas purge and consider low-temperature milling
- Increase mill temperature
- Use acidic cleaning agents
Correct Answer: Control humidity, use inert atmosphere or dry gas purge and consider low-temperature milling
Q50. Which outcome improves when particle size distribution is narrow and controlled after milling?
- Batch-to-batch variability and dose uniformity are improved
- Regulatory inspections become unnecessary
- Packaging costs increase exponentially
- API always becomes chemically more potent
Correct Answer: Batch-to-batch variability and dose uniformity are improved
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.
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