Introduction: The “Objectives of size reduction MCQs With Answer” resource is designed for B. Pharm students to master particle size reduction and comminution principles. This concise guide covers objectives of size reduction, particle size distribution, milling and grinding equipment, energy efficiency, and effects on dissolution, bioavailability, and stability. Ideal for exam preparation, these MCQs emphasize pharmaceutical milling, pulverization methods, wet vs. dry grinding, sieving, and scale-up considerations. By focusing on core goals—enhanced surface area, improved uniformity, and controlled particle size—the practice set reinforces theoretical concepts and practical selection of mills. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary objective of size reduction in pharmaceutical processing?
- To increase bulk density
- To reduce surface area
- To increase surface area for dissolution
- To change chemical composition
Correct Answer: To increase surface area for dissolution
Q2. Which term is synonymous with size reduction in engineering practice?
- Comminution
- Sublimation
- Annealing
- Polymerization
Correct Answer: Comminution
Q3. Which law relates energy required to particle size reduction and states energy is proportional to new surface area?
- Kick’s law
- Rittinger’s law
- Bond’s law
- Newton’s law
Correct Answer: Rittinger’s law
Q4. Bond’s law is most applicable for which size range?
- Very fine particles (<10 µm)
- Coarse to intermediate sizes
- Molecular size changes
- Only for liquids
Correct Answer: Coarse to intermediate sizes
Q5. Which objective of size reduction directly improves content uniformity in solid dosage forms?
- Increasing particle hardness
- Reducing interparticle forces
- Reducing particle size to achieve uniform mixing
- Changing crystal polymorph
Correct Answer: Reducing particle size to achieve uniform mixing
Q6. Which mill type is commonly used for fine grinding in the pharmaceutical industry?
- Hammer mill
- Ball mill
- Roller mill
- Cutting mill
Correct Answer: Ball mill
Q7. What is a key advantage of jet milling for pharmaceutical powders?
- High heat generation
- Contamination from grinding media
- Achieves submicron to micron sizes without media
- Low energy efficiency
Correct Answer: Achieves submicron to micron sizes without media
Q8. Which objective of size reduction helps enhance dissolution rate of poorly soluble drugs?
- Decrease surface area
- Increase particle size distribution breadth
- Increase surface area by reducing particle size
- Reduce porosity only
Correct Answer: Increase surface area by reducing particle size
Q9. Rittinger’s law best predicts energy consumption when:
- Large size changes occur
- Surface area change is negligible
- Very fine grinding predominates and new surface area increases significantly
- No particle breakage occurs
Correct Answer: Very fine grinding predominates and new surface area increases significantly
Q10. Which parameter is NOT a direct objective of size reduction?
- Improve dissolution
- Enhance flow properties
- Alter chemical structure
- Increase surface area
Correct Answer: Alter chemical structure
Q11. Which technique is used to determine particle size distribution after size reduction?
- Spectrophotometry
- Sieve analysis and laser diffraction
- Chromatography
- pH titration
Correct Answer: Sieve analysis and laser diffraction
Q12. What is a disadvantage of wet milling compared to dry milling?
- Lower heat generation
- Possible hydrolysis or degradation of moisture-sensitive drugs
- Improved dispersion
- Better control of agglomeration
Correct Answer: Possible hydrolysis or degradation of moisture-sensitive drugs
Q13. Which objective of size reduction is critical for improving content uniformity in low-dose formulations?
- Generating broad particle size distribution
- Producing narrow, uniform particle size
- Maximizing bulk density
- Increasing moisture content
Correct Answer: Producing narrow, uniform particle size
Q14. What is the main cause of heat generation during mechanical size reduction?
- Chemical reactions
- Friction and impact energy conversion to heat
- Evaporation of solvents
- Radiation absorption
Correct Answer: Friction and impact energy conversion to heat
Q15. Kick’s law suggests energy required for size reduction is proportional to:
- New surface area created
- Logarithm of size ratio
- Square of particle diameter
- Volume change only
Correct Answer: Logarithm of size ratio
Q16. Which mill uses rotating hammers to reduce particle size?
- Cone mill
- Hammer mill
- Jet mill
- Ball mill
Correct Answer: Hammer mill
Q17. Which objective of size reduction is essential for improving powder flow in tablet compression?
- Increasing fines content only
- Producing optimal particle shape and size distribution
- Maximizing electrostatic charge
- Creating highly irregular large particles
Correct Answer: Producing optimal particle shape and size distribution
Q18. Which parameter describes particle size by the diameter below which a given percentage of the sample lies (e.g., D50)?
- Specific surface area
- Median diameter
- Bulk density
- True density
Correct Answer: Median diameter
Q19. Which milling method avoids contamination from grinding media by using particles accelerated by gas streams?
- Ball milling
- Jet milling
- Roller milling
- Hammer milling
Correct Answer: Jet milling
Q20. An objective of size reduction in granulation is to:
- Increase tablet friability only
- Produce fines for direct compression without binders
- Create uniform granule size for better compressibility
- Increase hygroscopicity
Correct Answer: Create uniform granule size for better compressibility
Q21. What is a critical factor when selecting a mill for heat-sensitive drugs?
- Maximizing impact energy
- Minimizing heat generation and residence time
- Using the largest feed size possible
- Choosing the cheapest available mill
Correct Answer: Minimizing heat generation and residence time
Q22. Which size reduction objective helps in improving suspension stability in liquid formulations?
- Producing very large particles
- Reducing particle size to narrow distribution
- Increasing density differences
- Enhancing aggregation
Correct Answer: Reducing particle size to narrow distribution
Q23. What does specific surface area measure?
- Volume per particle
- Surface area per unit mass
- Bulk volume per bulk mass
- Number of particles per gram
Correct Answer: Surface area per unit mass
Q24. Which hazard is particularly important to control during powder size reduction?
- Thermal runaway of solvents only
- Dust explosion and inhalation risks
- Excessive cooling
- UV exposure
Correct Answer: Dust explosion and inhalation risks
Q25. Which instrument measures particle size using scattering of a laser beam?
- Sieve shaker
- Laser diffraction particle size analyzer
- Viscometer
- HPLC
Correct Answer: Laser diffraction particle size analyzer
Q26. Which objective of size reduction is important for improving drug absorption from oral formulations?
- Reducing dissolution rate
- Increasing particle size
- Enhancing surface area to improve dissolution and absorption
- Decreasing wettability
Correct Answer: Enhancing surface area to improve dissolution and absorption
Q27. What factor most influences the selection between wet and dry milling?
- Color of drug
- Moisture sensitivity and desired particle characteristics
- Brand of mill manufacturer
- Ambient humidity only
Correct Answer: Moisture sensitivity and desired particle characteristics
Q28. Which of the following is an objective of size reduction related to stability?
- Generate excessive mechanical energy to induce polymorphic changes
- Reduce particle size to reduce degradation solely
- Control particle size to minimize chemical instability and aggregation
- Increase surface area to accelerate degradation
Correct Answer: Control particle size to minimize chemical instability and aggregation
Q29. What is the effect of excessive fines produced during milling?
- Improved flow always
- Increased cohesion, poor flow, and segregation issues
- Reduced surface area
- No impact on downstream processing
Correct Answer: Increased cohesion, poor flow, and segregation issues
Q30. Which mill is especially suitable for producing uniform granules by shearing?
- Colloid mill
- Ball mill
- Hammer mill
- Jet mill
Correct Answer: Colloid mill
Q31. Which objective of size reduction impacts the taste and mouthfeel of oral powders?
- Particle color only
- Surface area and particle size influencing dissolution and texture
- Bulk density exclusively
- pH alteration
Correct Answer: Surface area and particle size influencing dissolution and texture
Q32. What is the importance of controlling particle shape during size reduction?
- Shape has no effect on flow or compaction
- Particle shape influences flow, packing, and compactibility
- Only color is influenced by shape
- Shape only affects chemical stability
Correct Answer: Particle shape influences flow, packing, and compactibility
Q33. What is the terminal objective when reducing particle size for inhalation aerosols?
- Produce large particles (>100 µm)
- Achieve aerodynamic diameter suitable for lung deposition (1–5 µm)
- Maximize bulk density for capsule filling
- Create sticky agglomerates
Correct Answer: Achieve aerodynamic diameter suitable for lung deposition (1–5 µm)
Q34. Which factor decreases the efficiency of a mill?
- Appropriate feed rate
- Excessive moisture causing clogging and agglomeration
- Optimal screen size
- Proper maintenance
Correct Answer: Excessive moisture causing clogging and agglomeration
Q35. Which measurement quantifies powder flowability often affected by size reduction?
- Zeta potential
- Angle of repose
- pKa
- Melting point
Correct Answer: Angle of repose
Q36. Which objective of size reduction is most relevant for controlled-release formulations?
- Increase dissolution of all components
- Tailor particle size to modify release rate and surface area
- Maximize fines for immediate release
- Ensure complete amorphization
Correct Answer: Tailor particle size to modify release rate and surface area
Q37. What is the effect of milling on crystal habit and solid-state form?
- No effect at all
- May induce polymorphic transitions or amorphization due to mechanical stress
- Always improves crystalline order
- Only affects color
Correct Answer: May induce polymorphic transitions or amorphization due to mechanical stress
Q38. Which screening device is used after milling to classify particle sizes?
- Centrifuge
- Sieve shaker or vibratory screen
- Refractometer
- Polarimeter
Correct Answer: Sieve shaker or vibratory screen
Q39. Which objective of size reduction helps in improving content uniformity during capsule filling?
- Produce very large irregular particles
- Reduce particle size and narrow distribution for uniform dosing
- Increase static electricity
- Create wide particle size distribution
Correct Answer: Reduce particle size and narrow distribution for uniform dosing
Q40. In stirred ball mills, which parameter most affects fineness achieved?
- Color of balls
- Rotation speed and grinding media size
- Ambient lighting
- Operator height
Correct Answer: Rotation speed and grinding media size
Q41. What is the purpose of cryogenic milling in pharmaceuticals?
- Increase temperature during milling
- Reduce brittleness
- Prevent thermal degradation and make materials brittle for easier fracture
- Introduce moisture
Correct Answer: Prevent thermal degradation and make materials brittle for easier fracture
Q42. Which objective of size reduction is important for improving homogeneity in powder blends with low-dose APIs?
- Encourage segregation by creating mixed sizes
- Match particle size of API and excipients to reduce segregation
- Increase electrostatic charge differences
- Maximize fines only
Correct Answer: Match particle size of API and excipients to reduce segregation
Q43. What does the term “breakage distribution” refer to in milling?
- Distribution of particle color post-milling
- Probability distribution of fragment sizes produced from parent particles
- Temperature distribution inside mill
- Distribution of operator shifts
Correct Answer: Probability distribution of fragment sizes produced from parent particles
Q44. Which parameter is crucial to measure when scaling up a milling process?
- Operator’s preference
- Specific energy input and residence time
- Room paint color
- Packaging material color
Correct Answer: Specific energy input and residence time
Q45. Which mill type is preferred for gentle size reduction of heat-sensitive botanical extracts?
- High-speed hammer mill
- Low-shear conical mill or cryogenic milling
- Open-top jaw crusher
- Direct-fired rotary kiln
Correct Answer: Low-shear conical mill or cryogenic milling
Q46. Which objective of size reduction assists in improving solubility through amorphization?
- Induce controlled amorphization by high-energy milling
- Increase crystallinity
- Reduce surface area
- Decrease wettability
Correct Answer: Induce controlled amorphization by high-energy milling
Q47. What is the effect of particle aggregation after milling?
- Always decreases effective particle size
- Can reduce effective surface area and affect dissolution
- Improves aerosol performance automatically
- Has no impact on stability
Correct Answer: Can reduce effective surface area and affect dissolution
Q48. Which objective is addressed by using coatings after size reduction?
- Hide particle color only
- Control taste, surface properties, and prevent agglomeration
- Increase bulk density drastically
- Convert particles into crystals
Correct Answer: Control taste, surface properties, and prevent agglomeration
Q49. What is the typical consequence of overgrinding a pharmaceutical powder?
- Improved flow and reduced cohesiveness always
- Excess fines, increased cohesion, potential stability issues and altered bioavailability
- No change in product performance
- Reduced surface area
Correct Answer: Excess fines, increased cohesion, potential stability issues and altered bioavailability
Q50. Which practice helps minimize contamination during milling?
- Using worn grinding media
- Regular maintenance, choosing appropriate mill materials, and using inert milling environments if needed
- Ignoring material compatibility
- Operating at maximum throughput regardless of conditions
Correct Answer: Regular maintenance, choosing appropriate mill materials, and using inert milling environments if needed
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