Understanding pharmaceutical problems involving dispersion is essential for B.Pharm students preparing for formulation and quality control. This topic covers fundamentals of pharmaceutical dispersions — suspensions, emulsions, and colloids — and focuses on critical issues such as particle size distribution, stability, flocculation, coalescence, sedimentation, Ostwald ripening, and zeta potential. Practical aspects include Stokes’ law, rheology, surfactant selection, HLB, wetting agents, homogenization, and measurement techniques for particle sizing and stability testing. This review integrates theory and practical problem-solving to strengthen exam readiness and laboratory skills. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the typical particle size range for colloidal dispersions?
- Less than 1 nm
- 1 nm to 1 µm
- 1 µm to 100 µm
- Greater than 100 µm
Correct Answer: 1 nm to 1 µm
Q2. Which phenomenon explains the visible scattering of light by colloidal particles?
- Brownian motion
- Ostwald ripening
- Tyndall effect
- Stokes’ settling
Correct Answer: Tyndall effect
Q3. Brownian motion in dispersions is primarily caused by:
- Gravity acting on particles
- Random collisions with solvent molecules
- Electrostatic attraction between particles
- Shear stress from mixing
Correct Answer: Random collisions with solvent molecules
Q4. According to Stokes’ law, sedimentation rate increases with:
- Decrease in particle density difference
- Increase in fluid viscosity
- Increase in particle radius squared
- Decrease in gravitational acceleration
Correct Answer: Increase in particle radius squared
Q5. Flocculation in suspensions refers to:
- Formation of a compact cake that is hard to redisperse
- Aggregation of particles into loose, reversible clusters
- Uniform dissolution of particles in the medium
- Complete chemical reaction between particles
Correct Answer: Aggregation of particles into loose, reversible clusters
Q6. Zeta potential is a measure of:
- Particle size distribution
- Electrical potential at the slipping plane of particles
- Viscosity of the dispersion medium
- Interfacial tension between phases
Correct Answer: Electrical potential at the slipping plane of particles
Q7. Which process reduces interfacial tension to stabilize emulsions?
- Adding electrolytes
- Using surfactants
- Increasing temperature only
- Decreasing particle size by milling
Correct Answer: Using surfactants
Q8. Ostwald ripening in dispersions refers to:
- Particle aggregation by flocculation
- Smaller particles dissolving and redepositing onto larger ones
- Phase inversion from O/W to W/O
- Immediate coalescence of droplets
Correct Answer: Smaller particles dissolving and redepositing onto larger ones
Q9. Creaming in emulsions is best described as:
- Permanent coalescence of droplets
- Migration of dispersed droplets to the top forming a concentrate
- Complete dissolution of dispersed phase
- Formation of solid aggregates
Correct Answer: Migration of dispersed droplets to the top forming a concentrate
Q10. Which parameter is commonly used to select an emulsifier for oil-in-water emulsions?
- HLB value of the emulsifier
- pKa of the oil phase
- Viscosity of the aqueous phase only
- Boiling point of the surfactant
Correct Answer: HLB value of the emulsifier
Q11. A high absolute zeta potential (positive or negative) generally indicates:
- Greater tendency for particle aggregation
- Less electrostatic repulsion between particles
- Improved colloidal stability due to stronger repulsion
- No relation to stability
Correct Answer: Improved colloidal stability due to stronger repulsion
Q12. Which method is commonly used for reducing particle size in suspensions?
- Centrifugation
- Wet milling (media milling)
- Freeze-drying
- Dialysis
Correct Answer: Wet milling (media milling)
Q13. The DLVO theory combines which interactions to explain colloidal stability?
- Van der Waals attraction and electrostatic repulsion
- Hydrophobic interaction and steric stabilization
- Viscous drag and Brownian motion
- Surface tension and osmotic pressure
Correct Answer: Van der Waals attraction and electrostatic repulsion
Q14. Which experimental technique measures particle size by light scattering?
- Ultracentrifugation
- Dynamic light scattering (DLS)
- Titration
- Infrared spectroscopy
Correct Answer: Dynamic light scattering (DLS)
Q15. Which of the following promotes wetting of hydrophobic drug particles by water?
- Adding water-immiscible oils
- Using surfactants or wetting agents
- Decreasing dispersion temperature only
- Increasing particle aggregation intentionally
Correct Answer: Using surfactants or wetting agents
Q16. Perikinetic coagulation is caused by:
- Brownian motion induced collisions
- Shear-induced collisions during stirring
- Electrostatic stabilization
- Chemical crosslinking of particles
Correct Answer: Brownian motion induced collisions
Q17. Which factor decreases sedimentation rate in suspensions?
- Increasing particle size
- Reducing medium viscosity
- Adding viscosity modifiers to the medium
- Increasing density difference between particle and medium
Correct Answer: Adding viscosity modifiers to the medium
Q18. Coalescence in emulsions results in:
- Droplets merging to form larger droplets
- Formation of a stable microemulsion
- Complete solubilization of oil in water
- Crystallization of dispersed phase
Correct Answer: Droplets merging to form larger droplets
Q19. Which emulsifier type is preferred for water-in-oil (W/O) emulsions?
- High HLB nonionic surfactant
- Low HLB lipophilic surfactant
- Highly water-soluble polymer only
- Strong electrolytes
Correct Answer: Low HLB lipophilic surfactant
Q20. Sedimentation volume (F) in suspensions is defined as:
- Volume of supernatant divided by total volume
- Height of sediment divided by original suspension height
- Viscosity of suspension divided by viscosity of medium
- Particle size divided by density difference
Correct Answer: Height of sediment divided by original suspension height
Q21. Which process is most likely to improve redispersibility of a flocculated suspension?
- Encouraging formation of a hard cake during storage
- Using flocculating agents to form loose aggregates
- Removing all surfactants
- Heating to evaporate the medium
Correct Answer: Using flocculating agents to form loose aggregates
Q22. Which factor does NOT directly affect emulsion stability?
- Interfacial tension between phases
- Droplet size distribution
- Color of the oil phase
- Viscosity of continuous phase
Correct Answer: Color of the oil phase
Q23. Homogenization of emulsions primarily aims to:
- Increase droplet size for better sedimentation
- Decrease droplet size and narrow size distribution
- Change chemical composition of oil
- Remove preservatives
Correct Answer: Decrease droplet size and narrow size distribution
Q24. Which is a common preservative challenge in aqueous suspensions and emulsions?
- Preservatives having no solubility issues
- Partitioning of preservative into the dispersed phase reducing efficacy
- Surfactants always increasing preservative activity
- Preservatives preventing particle wetting
Correct Answer: Partitioning of preservative into the dispersed phase reducing efficacy
Q25. An increase in ionic strength of the medium generally causes:
- Increase in zeta potential magnitude and stabilization
- Compression of electrical double layer and possible aggregation
- No change in interparticle interactions
- Immediate dissolution of particles
Correct Answer: Compression of electrical double layer and possible aggregation
Q26. Which rheological behavior is often desirable for suspensions to prevent rapid settling?
- Low viscosity Newtonian behavior
- Shear-thinning pseudoplastic behavior
- Highly thixotropic with permanent structure forming
- High dilatant behavior increasing viscosity under shear
Correct Answer: Shear-thinning pseudoplastic behavior
Q27. Peroxide formation in dispersed oils can be minimized by:
- Exposing emulsions to light and air during storage
- Adding antioxidants and storing under inert atmosphere
- Increasing amount of unsaturated oils
- Removing antioxidants
Correct Answer: Adding antioxidants and storing under inert atmosphere
Q28. Which technique separates particles based on size and density using centrifugal force?
- Dynamic light scattering
- Ultracentrifugation
- pH titration
- Thin layer chromatography
Correct Answer: Ultracentrifugation
Q29. Steric stabilization of colloids is achieved by:
- Increasing ionic strength to screen charges
- Adsorption of polymers or nonionic surfactants to provide a physical barrier
- Removing all adsorbed layers from particle surface
- Reducing medium viscosity drastically
Correct Answer: Adsorption of polymers or nonionic surfactants to provide a physical barrier
Q30. Which measurement directly assesses electrokinetic potential of dispersed particles?
- Viscometry
- Electrophoretic mobility measurement for zeta potential
- Gas chromatography
- UV-visible absorbance for turbidity
Correct Answer: Electrophoretic mobility measurement for zeta potential
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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