Densities of powders MCQs With Answer

Introduction: Understanding densities of powders is essential for B.Pharm students involved in formulation, quality control and dosage form design. This topic — densities of powders MCQs With Answer — covers bulk density, tapped density, true (particle) density, porosity, compressibility index (Carr’s index), Hausner ratio and measurement techniques like graduated cylinder method, tapped-density tester and helium pycnometry. Mastery of calculations, units (g/cm3 or g/mL), sources of error and the effects of particle size, shape, moisture and granulation on density helps predict powder flow, packing, die-fill and tablet performance. These MCQs with answers reinforce concepts, calculation practice and practical formulation significance. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the definition of bulk density of a powder?

• The mass of powder divided by the total volume it occupies including interparticulate voids
• The mass of powder divided by the true volume of solid material excluding pores
• The tapped mass after mechanical compaction divided by tapped volume
• The density measured by helium displacement

Correct Answer: The mass of powder divided by the total volume it occupies including interparticulate voids

Q2. Which best describes true (particle) density?

• Mass of powder divided by bulk volume including voids
• Mass of powder divided by the volume of the solid particles excluding interparticulate voids
• Tapped mass divided by tapped volume
• Density measured in a graduated cylinder

Correct Answer: Mass of powder divided by the volume of the solid particles excluding interparticulate voids

Q3. What is tapped density?

• Density measured without allowing particles to settle
• Density after mechanical tapping that reduces powder volume
• Density measured by helium pycnometry
• Density of a single particle measured microscopically

Correct Answer: Density after mechanical tapping that reduces powder volume

Q4. Which formula correctly gives porosity (ε) using bulk density (ρb) and true density (ρt)?

• ε = ρb / ρt
• ε = 1 – (ρb / ρt)
• ε = (ρt – ρb) / ρb
• ε = ρt / ρb

Correct Answer: ε = 1 – (ρb / ρt)

Q5. How is Carr’s compressibility index (%) calculated?

• (Bulk density – Tapped density) / Bulk density × 100
• (Tapped density – Bulk density) / Tapped density × 100
• (Tapped density / Bulk density) × 100
• (Bulk density / Tapped density) × 100

Correct Answer: (Tapped density – Bulk density) / Tapped density × 100

Q6. What is the Hausner ratio formula?

• Bussed density / Bulk density
• Tapped density / Bulk density
• Bulk density / Tapped density
• Tapped density – Bulk density

Correct Answer: Tapped density / Bulk density

Q7. Which unit is commonly used for powder densities in pharmaceutics?

• kg/m3 only
• g/cm3 or g/mL
• mol/L
• ppm

Correct Answer: g/cm3 or g/mL

Q8. Which instrument is most appropriate for measuring true particle density by gas displacement?

• Graduated cylinder
• Tapped-density tester
• Helium pycnometer
• Optical microscope

Correct Answer: Helium pycnometer

Q9. Why is helium preferred in a pycnometer for true density measurement?

• Helium dissolves many organic powders for better measurement
• Helium molecules are small and penetrate open pores to measure solid volume accurately
• Helium is liquid at room temperature and fills closed pores
• Helium increases bulk volume for easier reading

Correct Answer: Helium molecules are small and penetrate open pores to measure solid volume accurately

Q10. If 50 g of powder occupies a bulk volume of 200 mL, what is the bulk density?

• 0.10 g/mL
• 0.25 g/mL
• 2.50 g/mL
• 4.00 g/mL

Correct Answer: 0.25 g/mL

Q11. If the same 50 g powder after tapping occupies 150 mL, what is the tapped density?

• 0.33 g/mL
• 0.50 g/mL
• 0.25 g/mL
• 1.50 g/mL

Correct Answer: 0.33 g/mL

Q12. Using bulk density 0.25 g/mL and tapped density 0.33 g/mL, what is Carr’s index (%) approximately?

• 5%
• 25%
• 50%
• 75%

Correct Answer: 25%

Q13. Using the same densities (bulk 0.25, tapped 0.33), what is the Hausner ratio approximately?

• 0.75
• 1.33
• 2.00
• 3.00

Correct Answer: 1.33

Q14. A powder has bulk density 0.6 g/mL and true density 1.2 g/mL. What is porosity?

• 0.2 or 20%
• 0.5 or 50%
• 1.8 or 180%
• 0.05 or 5%

Correct Answer: 0.5 or 50%

Q15. How does irregular particle shape generally affect bulk density and flow?

• Increases packing efficiency and improves flow
• Increases interparticle voids, reducing bulk density and worsening flow
• Has no effect on bulk density or flow
• Makes powders dissolve faster but does not change density

Correct Answer: Increases interparticle voids, reducing bulk density and worsening flow

Q16. Which Carr’s index range indicates excellent flow?

• < 15%
• 15–25%
• 25–35%
• > 35%

Correct Answer: < 15%

Q17. What is the common effect of small amounts of moisture on powder flow?

• Always improves flow by lubrication
• Increases interparticle cohesion and reduces flowability
• Transforms powder into a gas
• Has no measurable effect on powder properties

Correct Answer: Increases interparticle cohesion and reduces flowability

Q18. Which density parameter most directly affects die fill and tablet weight uniformity?

• True density only
• Bulk density
• Color density
• Optical density

Correct Answer: Bulk density

Q19. Which apparatus is used to determine tapped density experimentally?

• Tap density tester (tapped-volume apparatus)
• pH meter
• UV-Vis spectrophotometer
• Melting point apparatus

Correct Answer: Tap density tester (tapped-volume apparatus)

Q20. Why are powder density measurements critical in formulation development?

• Only to determine color stability
• To predict flow, packing, compression behavior and to optimize processing
• To measure antimicrobial activity
• To determine melting point

Correct Answer: To predict flow, packing, compression behavior and to optimize processing

Q21. True density is primarily dependent on which factor?

• Packing method used in the container
• Material composition and intrinsic solid structure
• Tapper speed only
• Color of the formulation

Correct Answer: Material composition and intrinsic solid structure

Q22. Which simple lab method is commonly used to measure apparent (bulk) density?

• Graduated cylinder method by pouring powder and reading volume
• High-performance liquid chromatography
• Infrared spectroscopy
• Atomic absorption spectroscopy

Correct Answer: Graduated cylinder method by pouring powder and reading volume

Q23. Tapped density data are used primarily to calculate which of the following?

• pKa of the drug
• Compressibility index and Hausner ratio
• Surface tension of liquids
• Viscosity of suspensions

Correct Answer: Compressibility index and Hausner ratio

Q24. Which Hausner ratio value indicates very poor flow?

• < 1.2
• 1.2–1.3
• > 1.4
• Exactly 1.0

Correct Answer: > 1.4

Q25. What is the usual effect of wet granulation on bulk density and flow?

• Decreases bulk density and worsens flow
• Increases bulk density and improves flowability and compressibility
• Turns powder into a gas
• Has no effect on powder properties

Correct Answer: Increases bulk density and improves flowability and compressibility

Q26. Which density measurement includes interparticulate voids?

• True density
• Bulk density
• Particle skeletal density
• Atomic density

Correct Answer: Bulk density

Q27. The Hausner ratio is directly calculated as:

• Bulk density / Tapped density
• Tapped density × Bulk density
• Tapped density / Bulk density
• Bulk density – Tapped density

Correct Answer: Tapped density / Bulk density

Q28. A powder has a Carr’s index of 35%. What does this indicate about flowability?

• Excellent flow
• Good flow
• Fair flow
• Poor to very poor flow

Correct Answer: Poor to very poor flow

Q29. Which liquid is commonly used in liquid-displacement pycnometry for non-swelling pharmaceutical powders?

• Water for all powders
• Toluene (non-polar, non-swelling solvent)
• Concentrated acid
• Strong base

Correct Answer: Toluene (non-polar, non-swelling solvent)

Q30. Which of the following is NOT a typical source of error in powder density measurements?

• Inconsistent pouring technique when filling a graduated cylinder
• Static charge causing volume expansion
• Incorrect sample mass recording
• Color of the powder

Correct Answer: Color of the powder