Flow properties of powders MCQs With Answer

Introduction: Understanding the flow properties of powders is essential in pharmaceutics for tablet manufacturing, capsule filling, and consistent dosing. Key concepts include angle of repose, bulk density, tapped density, Carr’s index, Hausner ratio, particle size and shape, interparticle forces, cohesiveness, compressibility, and use of glidants or lubricants. Laboratory methods—angle of repose measurement, tapped density tester, shear cell, and flow rate through hoppers—help predict performance during processing and scale-up. Mastery of these parameters enables formulation optimization, selection of excipients, and problem solving for poor flow. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What does the angle of repose primarily indicate about a powder?

• Its chemical stability
• Its flowability and interparticle friction
• Its moisture content
• Its compressibility under high pressure

Correct Answer: Its flowability and interparticle friction

Q2. Which pair of measurements is required to calculate Carr’s compressibility index?

• Particle size and particle shape
• Bulk density and tapped density
• Angle of repose and Hausner ratio
• True density and porosity

Correct Answer: Bulk density and tapped density

Q3. How is the Hausner ratio calculated?

• Bulk density divided by tapped density
• Tapped density divided by bulk density
• Angle of repose divided by 10
• True density minus bulk density

Correct Answer: Tapped density divided by bulk density

Q4. A powder with Hausner ratio of 1.10 would be classified as having:

• Very poor flow
• Good flow
• Very sticky behavior
• Extremely high compressibility

Correct Answer: Good flow

Q5. Typical interpretation: Carr’s index less than 15% indicates:

• Very poor flow properties
• Excellent flow properties
• High cohesion and sticking
• Excessive moisture content

Correct Answer: Excellent flow properties

Q6. Which excipient is commonly used as a glidant to improve powder flow?

• Magnesium stearate
• Colloidal silicon dioxide (colloidal silica)
• Lactose monohydrate
• Hydroxypropyl methylcellulose (HPMC)

Correct Answer: Colloidal silicon dioxide (colloidal silica)

Q7. Which instrument directly measures powder flow under consolidated and uniaxial stress to give a flow function?

• Tap density tester
• Angle of repose apparatus
• Shear cell (e.g., Schulze tester)
• Pycnometer

Correct Answer: Shear cell (e.g., Schulze tester)

Q8. What effect does a broad particle size distribution generally have on powder flow?

• Always worsens flowability
• Can improve packing and flow by filling interstitial voids
• Makes the powder chemically reactive
• Eliminates electrostatic charging completely

Correct Answer: Can improve packing and flow by filling interstitial voids

Q9. Which of the following is NOT a cause of poor powder flow?

• High cohesion due to fines
• Irregular particle shape
• Low humidity and dryness
• Electrostatic charges between particles

Correct Answer: Low humidity and dryness

Q10. The tapped density is measured to determine:

• Powder chemical purity
• Volume reduction upon mechanical tapping
• Angle of internal friction
• True particle density without voids

Correct Answer: Volume reduction upon mechanical tapping

Q11. Which flow parameter directly quantifies the ease with which a powder consolidates under pressure?

• Angle of repose
• Flow function (ffc)
• True density
• pH of the powder slurry

Correct Answer: Flow function (ffc)

Q12. How does adding a small amount of lubricant like magnesium stearate typically affect powder flow and tablet compaction?

• Improves flow but may reduce tablet tensile strength if overused
• Worsens flow and always increases tablet strength
• Has no effect on either property
• Eliminates the need for glidants

Correct Answer: Improves flow but may reduce tablet tensile strength if overused

Q13. Which surface property increases interparticle attraction and often reduces flowability?

• Hydrophobicity
• High surface energy leading to adhesion and van der Waals forces
• Low specific surface area
• Perfect sphericity

Correct Answer: High surface energy leading to adhesion and van der Waals forces

Q14. In angle of repose measurement using a fixed funnel method, a lower angle indicates:

• Poor flow due to cohesive forces
• Better flow and lower interparticle friction
• Higher moisture absorption
• Higher compressibility index

Correct Answer: Better flow and lower interparticle friction

Q15. What is the main practical purpose of measuring bulk and tapped densities in formulation development?

• To estimate compressibility and predict filling behavior in hoppers and dies
• To determine chemical degradation pathways
• To calculate dissolution rate constants directly
• To measure tablet disintegration time

Correct Answer: To estimate compressibility and predict filling behavior in hoppers and dies

Q16. Which particle shape favors the best powder flow?

• Fibrous and elongated particles
• Flaky irregular particles
• Smooth, near-spherical particles
• Highly angular crystalline fragments

Correct Answer: Smooth, near-spherical particles

Q17. An increase in humidity often causes what effect on cohesive powders?

• Decrease in cohesion and improved flow
• Formation of liquid bridges, increasing cohesion and reducing flow
• Immediate chemical decomposition
• Reduction of particle size

Correct Answer: Formation of liquid bridges, increasing cohesion and reducing flow

Q18. What does a high Carr’s index (e.g., >25%) imply about a powder?

• Excellent flowability and low compressibility
• Poor flowability and high compressibility
• High true density and low porosity
• Low tendency to compact under pressure

Correct Answer: Poor flowability and high compressibility

Q19. Which technique is commonly used to improve flowability by increasing particle size and creating granules?

• Lyophilization
• Granulation (wet or dry)
• Micronization
• Spray drying to produce ultrafine powder

Correct Answer: Granulation (wet or dry)

Q20. The flow rate through a hopper is mostly influenced by:

• Ambient light intensity
• Wall friction, powder cohesion, and hopper geometry
• Chemical reactivity of the powder with air
• Color of the powder

Correct Answer: Wall friction, powder cohesion, and hopper geometry

Q21. In pharmaceutical practice, which property is most critical for uniform die filling in tablet compression?

• True density only
• Good powder flowability and consistent bulk density
• Low melting point
• High electrical conductivity

Correct Answer: Good powder flowability and consistent bulk density

Q22. Which measurement gives information about interparticle adhesive forces and bulk failure under stress?

• Angle of repose
• Shear cell testing (yield locus and cohesion)
• pH measurement of a powder slurry
• Optical rotation

Correct Answer: Shear cell testing (yield locus and cohesion)

Q23. Which statement about particle size reduction by milling is TRUE regarding powder flow?

• Milling always improves flow by making particles smaller
• Excessive reduction increases fines and may worsen flow due to cohesion
• Milling has no effect on flowability
• Smaller particles never contribute to segregation

Correct Answer: Excessive reduction increases fines and may worsen flow due to cohesion

Q24. What is the typical unit for expressing bulk and tapped densities?

• g/mL or g/cm³
• mol/L
• ppm
• KPa

Correct Answer: g/mL or g/cm³

Q25. Which additive can reduce interparticle friction and improve flow but must be used sparingly to avoid interference with tablet properties?

• Colloidal silicon dioxide used at very high concentrations
• Magnesium stearate (lubricant)
• Sodium chloride as a filler
• Hydrochloric acid

Correct Answer: Magnesium stearate (lubricant)

Q26. What is the relationship between true density, bulk density, and porosity of a powder bed?

• Porosity = 1 – (Bulk density / True density)
• True density = Bulk density + Porosity
• Bulk density = True density × Porosity
• Porosity and densities are unrelated

Correct Answer: Porosity = 1 – (Bulk density / True density)

Q27. Which powder property is LEAST likely to be measured by a tapped density tester?

• Tapped density value
• Compressibility index calculation
• Angle of repose
• Change in volume on tapping

Correct Answer: Angle of repose

Q28. During formulation, segregation of powders is often reduced by:

• Using a mixture of very different particle sizes
• Making particle sizes and densities more uniform or by granulation
• Increasing electrostatic charges intentionally
• Reducing binder content to zero

Correct Answer: Making particle sizes and densities more uniform or by granulation

Q29. Which flowability indicator is most appropriate for quick qualitative lab assessment of powder flow?

• Shear cell flow function measured over many hours
• Angle of repose measurement
• High-performance liquid chromatography
• Transmission electron microscopy

Correct Answer: Angle of repose measurement

Q30. What is a potential negative effect of excessive use of colloidal silica as a glidant?

• Complete dissolution of actives
• Insufficient lubrication leading to tablet sticking
• Increased segregation and difficulty in content uniformity if overdosed
• Instant disintegration of tablets

Correct Answer: Increased segregation and difficulty in content uniformity if overdosed