Classification of dispersed systems MCQs With Answer

Understanding the Classification of Dispersed Systems MCQs With Answer is essential for B.Pharm students preparing for exams and practical applications in pharmaceutics. This concise, SEO-friendly introduction covers key terms like dispersed systems, colloids, emulsions, suspensions, particle size, stability, and formulation strategies. Emphasis is placed on classification criteria (particle size, phase distribution, interaction with dispersion medium), stabilization mechanisms (surfactants, zeta potential, steric/electrostatic stabilization) and pharmaceutical relevance such as drug delivery and dosage form behavior. Clear, focused MCQs help reinforce theory and application, improving recall and problem-solving skills. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary basis for classifying dispersed systems?

• Chemical composition of solute
• Particle size of dispersed phase
• pH of dispersion medium
• Viscosity of dispersion medium

Correct Answer: Particle size of dispersed phase

Q2. Which particle size range typically defines colloidal dispersions?

• Less than 1 nanometer
• 1 nm to 1000 nm (1 μm)
• 1 μm to 100 μm
• Greater than 100 μm

Correct Answer: 1 nm to 1000 nm (1 μm)

Q3. Which of the following is an example of a true solution rather than a dispersed system?

• Sodium chloride in water at molecular level
• Milk (emulsion)
• Colloidal silica in water
• Suspension of talc in water

Correct Answer: Sodium chloride in water at molecular level

Q4. Which dispersed system is characterized by gas dispersed in a liquid?

• Emulsion
• Foam
• Aerosol
• Gel

Correct Answer: Foam

Q5. What phenomenon is used to detect colloidal particles by scattering of light?

• Brownian motion
• Tyndall effect
• Ostwald ripening
• Coagulation

Correct Answer: Tyndall effect

Q6. Brownian motion in colloids is primarily caused by:

• Gravitational settling of particles
• Thermal motion of solvent molecules colliding with particles
• Chemical reactions between phases
• Application of electric field

Correct Answer: Thermal motion of solvent molecules colliding with particles

Q7. Which class of dispersed systems contains oil droplets in water?

• W/O emulsion
• O/W emulsion
• Suspension
• Foam

Correct Answer: O/W emulsion

Q8. A dispersion where both dispersed phase and dispersion medium are liquids is called:

• Suspension
• Emulsion
• Sols
• Solid solution

Correct Answer: Emulsion

Q9. Which mechanism primarily stabilizes lyophilic colloids?

• Electrostatic repulsion
• Steric stabilization by solvent layers
• Magnetic forces
• Hydrodynamic shear

Correct Answer: Steric stabilization by solvent layers

Q10. What is the role of surfactants in emulsions?

• Increase particle size of dispersed phase
• Reduce interfacial tension and stabilize droplets
• Accelerate coalescence
• Convert emulsion into suspension

Correct Answer: Reduce interfacial tension and stabilize droplets

Q11. Which measurement provides information about particle charge and stability in colloids?

• pH measurement
• Zeta potential
• Viscosity
• Refractive index

Correct Answer: Zeta potential

Q12. Ostwald ripening is a process where:

• Large droplets shrink while small droplets grow
• Small particles dissolve and redeposit on larger particles
• Particles become electrically charged
• Particles form a crystalline lattice

Correct Answer: Small particles dissolve and redeposit on larger particles

Q13. Which class of dispersed systems has solid particles dispersed in gas?

• Aerosol (solid in gas)
• Emulsion
• Gel
• Suspension

Correct Answer: Aerosol (solid in gas)

Q14. The DLVO theory explains stability of colloidal systems by considering which two opposing forces?

• Van der Waals attraction and gravitational force
• Electrostatic repulsion and hydrophobic interaction
• Van der Waals attraction and electrostatic repulsion
• Steric hindrance and osmotic pressure

Correct Answer: Van der Waals attraction and electrostatic repulsion

Q15. Which instrument is commonly used to measure particle size distribution in dispersions?

• pH meter
• Dynamic light scattering (DLS)
• Ultraviolet spectrophotometer
• Osmometer

Correct Answer: Dynamic light scattering (DLS)

Q16. What does HLB (Hydrophile-Lipophile Balance) number help to select?

• Type of preservative for suspensions
• Appropriate surfactant for emulsification
• pH adjustment for buffer systems
• Viscosity modifier for gels

Correct Answer: Appropriate surfactant for emulsification

Q17. Which phenomenon leads to upward movement of oil droplets in an O/W emulsion?

• Creaming
• Coalescence
• Flocculation
• Ostwald ripening

Correct Answer: Creaming

Q18. Flocculation in suspensions refers to:

• Individual particles merging to form larger single particles
• Reversible aggregation into loose clusters
• Complete dissolution of particles
• Transformation into a gel

Correct Answer: Reversible aggregation into loose clusters

Q19. Which surfactant type is preferred to form oil-in-water emulsions?

• Lipophilic surfactant with low HLB
• Hydrophilic surfactant with high HLB
• Stermic surfactant with no HLB
• Amphoteric surfactant only

Correct Answer: Hydrophilic surfactant with high HLB

Q20. A sol is best described as:

• Liquid dispersed in gas
• Solid dispersed in liquid forming a colloidal suspension
• Gas dispersed in solid
• Two immiscible liquids mixed at molecular level

Correct Answer: Solid dispersed in liquid forming a colloidal suspension

Q21. Which term describes a semisolid system with a continuous liquid phase and a three-dimensional network?

• Emulsion
• Gel
• Foam
• Solution

Correct Answer: Gel

Q22. Which test distinguishes between true solutions and colloidal dispersions?

• Filterability through filter paper
• Tyndall effect (light scattering)
• Measurement of density
• Visual color observation

Correct Answer: Tyndall effect (light scattering)

Q23. In pharmaceutical suspensions, a suspending agent is added primarily to:

• Increase solubility of drug
• Prevent rapid sedimentation of particles
• Increase drug absorption rate
• Change color of formulation

Correct Answer: Prevent rapid sedimentation of particles

Q24. Which factor does NOT directly affect sedimentation rate according to Stokes’ law?

• Viscosity of medium
• Density difference between particle and medium
• Particle radius
• pH of the medium

Correct Answer: pH of the medium

Q25. Association colloids such as micelles form when surfactant concentration exceeds:

• Critical aggregation value (CAV)
• Critical micelle concentration (CMC)
• Hydrophile-lipophile threshold (HLT)
• Maximum solubility limit

Correct Answer: Critical micelle concentration (CMC)

Q26. Which process describes irreversible aggregation leading to particle settling and tight packing?

• Flocculation
• Coalescence
• Coagulation (or deflocculation leading to coagulation)
• Brownian stabilization

Correct Answer: Coagulation (or deflocculation leading to coagulation)

Q27. Which dispersed system classification is based on the physical state of the dispersed phase and dispersion medium?

• Chemical classification
• Phase-system classification (e.g., solid-in-liquid, liquid-in-liquid)
• pH-based classification
• Temperature-based classification

Correct Answer: Phase-system classification (e.g., solid-in-liquid, liquid-in-liquid)

Q28. Which of the following is an example of a lyophilic colloid in pharmaceutics?

• Starch sol
• Metallic nanoparticle sol with no hydration layer
• Hydrophobically coated silica
• Carbon black suspension

Correct Answer: Starch sol

Q29. Emulsions used for topical delivery often require which additive to increase viscosity and prevent phase separation?

• Preservative
• Wetting agent
• Thickening agent (e.g., carbomer)
• Salt

Correct Answer: Thickening agent (e.g., carbomer)

Q30. Which property helps colloidal particles resist sedimentation by thermal motion?

• High density
• Brownian motion
• Large particle size
• High ionic strength

Correct Answer: Brownian motion

Q31. Which term describes the separation of an emulsion into distinct layers of oil and water?

• Flocculation
• Coalescence leading to phase separation
• Creaming without phase separation
• Gelation

Correct Answer: Coalescence leading to phase separation

Q32. Which stabilizing mechanism is dominant when polymer chains adsorb onto particle surfaces to prevent aggregation?

• Electrostatic stabilization
• Steric stabilization
• Van der Waals attraction
• Hydrophobic collapse

Correct Answer: Steric stabilization

Q33. Which of the following is a method to prepare fine dispersions or emulsions in pharmacy?

• High-pressure homogenization
• Cold fusion without mixing
• Dry heating of components
• Static compression molding

Correct Answer: High-pressure homogenization

Q34. Which factor increases the rate of Ostwald ripening in emulsions?

• Use of low-solubility dispersed phase
• Use of highly soluble dispersed phase in continuous phase
• High viscosity medium
• Strong steric stabilizers

Correct Answer: Use of highly soluble dispersed phase in continuous phase

Q35. In a w/o emulsion, the continuous phase is:

• Water
• Oil
• Gas
• Solid

Correct Answer: Oil

Q36. Which phenomenon causes reversible aggregation that can be redispered by shaking?

• Coagulation
• Flocculation
• Irreversible coalescence
• Ostwald ripening

Correct Answer: Flocculation

Q37. What is the main pharmaceutical concern with creaming of emulsions?

• Loss of drug chemical stability
• Appearance change and non-uniform dosing if not redispersed
• Immediate microbial contamination
• pH changes in the emulsion

Correct Answer: Appearance change and non-uniform dosing if not redispersed

Q38. Which colloidal system is formed by association of amphiphilic molecules into spherical structures above CMC?

• Nanoliposomes
• Micelles
• Gels
• Foams

Correct Answer: Micelles

Q39. In suspensions, particle size reduction typically improves:

• Stability against aggregation only
• Sedimentation rate by increasing it
• Redispersibility and apparent dissolution rate
• Color stability only

Correct Answer: Redispersibility and apparent dissolution rate

Q40. Which of the following is NOT a classification criterion for dispersed systems?

• Particle size
• Nature of phases (solid/liquid/gas)
• Chemical formula of solute at atomic level
• Interaction with dispersion medium (lyophilic/lyophobic)

Correct Answer: Chemical formula of solute at atomic level

Q41. Which pharmaceutical dosage form is essentially a coarse dispersion of insoluble drug particles in a liquid?

• Syrup
• Suspension
• Solution
• Emulsion

Correct Answer: Suspension

Q42. Which stabilization strategy reduces electrostatic attraction between droplets by creating an energetic barrier?

• Adding salts to screen charges
• Increasing temperature drastically
• Adding electrolytes to cause coagulation
• Maintaining a zeta potential magnitude high enough for repulsion

Correct Answer: Maintaining a zeta potential magnitude high enough for repulsion

Q43. Which of the following is a common emulsifying agent used in oral emulsions?

• Liquid paraffin alone
• Sodium lauryl sulfate (anionic surfactant)
• Cetostearyl alcohol (as sole component)
• Silicon dioxide powder

Correct Answer: Sodium lauryl sulfate (anionic surfactant)

Q44. Which dispersed system can exhibit thixotropic behavior used in topical formulations?

• True solution
• Thixotropic gel or emulgel
• Rigid crystalline suspension
• Non-Newtonian gas mixture

Correct Answer: Thixotropic gel or emulgel

Q45. Which parameter increases when particles are highly charged and remain dispersed due to strong repulsive forces?

• Aggregation rate
• Zeta potential magnitude
• Coalescence propensity
• Solubility in nonpolar solvents

Correct Answer: Zeta potential magnitude

Q46. Microemulsions differ from macroemulsions mainly by being:

• Thermodynamically unstable and opaque
• Thermodynamically stable, transparent, and very small droplet size
• Solid dispersions rather than liquid
• Suspensions of large particles

Correct Answer: Thermodynamically stable, transparent, and very small droplet size

Q47. Which physical test would best assess creaming tendency of an emulsion?

• pH titration
• Accelerated centrifugation and visual observation
• Measuring refractive index only
• Checking smell for rancidity

Correct Answer: Accelerated centrifugation and visual observation

Q48. Which of the following describes a Pickering emulsion?

• Emulsion stabilized by solid particles adsorbed at the interface
• Emulsion stabilized exclusively by ionic surfactants
• Emulsion with no surfactant or stabilizer
• Emulsion stabilized by increasing temperature

Correct Answer: Emulsion stabilized by solid particles adsorbed at the interface

Q49. Which technique can be used to determine zeta potential of colloidal particles?

• Ultracentrifugation
• Electrophoretic light scattering
• Thermogravimetric analysis
• Infrared spectroscopy

Correct Answer: Electrophoretic light scattering

Q50. For parenteral nanoparticle formulations, which dispersed system property is most critical to avoid capillary occlusion?

• High polydispersity and large particle size fraction
• High color intensity
• Low pH only
• Presence of electrolytes

Correct Answer: High polydispersity and large particle size fraction

G S Sachin

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.

Mail- Sachin@pharmacyfreak.com