Determination of fineness of cosmetic powders MCQs With Answer

Introduction:

This quiz set on Determination of fineness of cosmetic powders is designed for M.Pharm students studying Herbal and Cosmetic Analysis (MPA 204T). It focuses on theoretical principles, commonly used analytical techniques (sieving, laser diffraction, microscopy, Coulter counting, sedimentation), sample preparation, and the practical implications of particle size on cosmetic performance and safety. Questions emphasize instrument selection, interpretation of particle-size data, pharmacopeial approaches, and troubleshooting deagglomeration and dispersion. Use these multiple-choice questions to test comprehension, prepare for viva or exams, and reinforce the deeper analytical considerations needed when assessing fineness in cosmetic powder formulations.

Q1. Which pharmacopeial method is classically used for determination of fineness of cosmetic powders?

• Sieving (sieve analysis)
• Optical microscopy
• Laser diffraction
• Dynamic light scattering

Correct Answer: Sieving (sieve analysis)

Q2. What is the basic principle behind laser diffraction particle size analysis?

• Measurement of Brownian motion to infer size
• Separation by centrifugal force
• Light scattering and diffraction pattern analysis
• Electrical impedance pulse counting

Correct Answer: Light scattering and diffraction pattern analysis

Q3. Which law relates settling velocity of a spherical particle in a fluid to its diameter, fluid viscosity and density difference?

• Hagen–Poiseuille law
• Stokes’ law
• Darcy’s law
• Fick’s law

Correct Answer: Stokes’ law

Q4. What is the approximate opening size of a 325-mesh sieve commonly used in cosmetic powder fineness testing?

• Approximately 250 micrometres (µm)
• Approximately 150 micrometres (µm)
• Approximately 75 micrometres (µm)
• Approximately 45 micrometres (µm)

Correct Answer: Approximately 45 micrometres (µm)

Q5. Which analytical technique primarily yields a volume-weighted particle size distribution useful for cosmetics?

• Optical microscopy counting
• Laser diffraction (provides volume-weighted size distribution)
• Dynamic light scattering (intensity-weighted)
• BET nitrogen adsorption (surface area)

Correct Answer: Laser diffraction (provides volume-weighted size distribution)

Q6. Which method is most suitable for measuring submicron fractions (below ~1 µm) in cosmetic dispersions?

• Sieving
• Optical microscopy
• Dynamic light scattering (photon correlation spectroscopy)
• Air jet sieving

Correct Answer: Dynamic light scattering (photon correlation spectroscopy)

Q7. Which powder characteristic is most directly improved by reducing the particle size in face powders?

• Chemical stability
• Spreadability and tactile smoothness
• pH of the formulation
• Color fastness to UV

Correct Answer: Spreadability and tactile smoothness

Q8. Which instrument counts particles by detecting changes in electrical resistance as particles pass through an aperture?

• Coulter counter (electrical sensing zone method)
• Laser diffraction analyzer
• Scanning electron microscope
• Optical image analyzer

Correct Answer: Coulter counter (electrical sensing zone method)

Q9. When preparing hydrophilic cosmetic powders for wet dispersion prior to particle sizing, which dispersant is generally appropriate?

• Non-polar oil only (no surfactant)
• Ethanol without any surfactant
• Water with a suitable surfactant
• Pure glycerin without mixing aid

Correct Answer: Water with a suitable surfactant

Q10. In sieve analysis, how is “residue on sieve” typically expressed?

• As the volume of retained particles in mL
• As mass retained on the sieve expressed as percentage of the sample
• As the number of particles retained per unit time
• As the mean diameter in micrometres

Correct Answer: As mass retained on the sieve expressed as percentage of the sample

Q11. What is a common practical consequence of reducing particle size excessively in cosmetic powders?

• Decreased moisture adsorption and less caking
• Increased caking due to higher surface area and moisture adsorption
• Lower adhesion to skin
• Immediate loss of color

Correct Answer: Increased caking due to higher surface area and moisture adsorption

Q12. Which pharmacopoeial test is most relevant for fineness assessment of talc used in cosmetics?

• Tapped density test
• Fineness by sieving (pharmacopoeial method)
• Melting point determination
• pH measurement of dispersion

Correct Answer: Fineness by sieving (pharmacopoeial method)

Q13. Which microscopy technique is most informative for assessing particle surface morphology and shape in cosmetic powders?

• Transmission electron microscopy (TEM)
• Scanning electron microscopy (SEM) for surface morphology and particle shape
• Optical microscopy with bright field only
• Polarimetry

Correct Answer: Scanning electron microscopy (SEM) for surface morphology and particle shape

Q14. Which technique typically provides a number-weighted particle size distribution, useful when particle count matters?

• Laser diffraction
• Coulter counter
• BET surface area
• Air permeability

Correct Answer: Coulter counter

Q15. For irregularly shaped cosmetic particles, which descriptor approximates particle size for comparison purposes?

• Aspect ratio only
• Optical density
• Equivalent spherical diameter
• pKa value

Correct Answer: Equivalent spherical diameter

Q16. Which operational variable must be controlled closely to obtain reproducible sieve analysis results?

• Ambient light intensity
• Colour of the powder
• Sieve shaking time and sample loading
• Magnetic field around the sieve

Correct Answer: Sieve shaking time and sample loading

Q17. Which sieving technique is suitable for separating and evaluating very fine, cohesive cosmetic powders?

• Wet sieving with no agitation
• Air jet sieving
• Coarse pan sieving only
• Manual tapping on a bench

Correct Answer: Air jet sieving

Q18. What is a recommended step to deagglomerate cosmetic powders before laser diffraction measurement?

• Measure as-is without dispersion
• Heating to high temperature to burn binders
• Disperse in appropriate medium with sonication and surfactant to deagglomerate
• Additive-free settling for 24 hours only

Correct Answer: Disperse in appropriate medium with sonication and surfactant to deagglomerate

Q19. Which safety concern is most relevant when handling ultrafine cosmetic powders in the lab?

• Explosion risk in aqueous solutions
• Respiratory inhalation hazard and possible pulmonary deposition
• High electrical conductivity causing shocks
• Radioactivity

Correct Answer: Respiratory inhalation hazard and possible pulmonary deposition

Q20. Which property is NOT directly obtained from a simple sieve analysis of a cosmetic powder?

• Mass percentage retained on each sieve
• Coarse/fine fraction percentages
• Specific surface area (requires BET or gas adsorption)
• Qualitative particle size distribution by size class

Correct Answer: Specific surface area (requires BET or gas adsorption)

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