Emulsions – theories of emulsification MCQs With Answer

Emulsions – theories of emulsification MCQs With Answer

Emulsions are biphasic systems central to pharmaceutics, drug delivery, and formulation science. This focused introduction for B. Pharm students covers theories of emulsification including interfacial tension reduction, DLVO theory, Bancroft’s rule, HLB concept, phase inversion and Pickering stabilization. Emphasis is on mechanisms affecting emulsion formation and stability—steric and electrostatic stabilization, coalescence, creaming, and microemulsion vs macroemulsion behavior—plus practical considerations like emulsifying agents, equipment, and temperature effects. SEO keywords: emulsions, theories of emulsification, emulsifying agents, HLB, DLVO, phase inversion, B. Pharm, pharmaceutics. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which statement best describes an emulsion?

• A thermodynamically stable single-phase solution
• A dispersion of fine solid particles in a liquid
• A biphasic system of two immiscible liquids with one dispersed in the other
• A gas dispersed in a liquid continuous phase

Correct Answer: A biphasic system of two immiscible liquids with one dispersed in the other

Q2. According to Bancroft’s rule, the phase in which the emulsifier is more soluble tends to be the continuous phase. This explains why:

• An emulsifier with higher oil solubility favors O/W emulsions
• An emulsifier with higher water solubility favors O/W emulsions
• An emulsifier’s solubility has no effect on phase distribution
• Emulsifier solubility only affects droplet size, not phase type

Correct Answer: An emulsifier with higher water solubility favors O/W emulsions

Q3. The Hydrophilic-Lipophilic Balance (HLB) value of an emulsifier indicates:

• The melting point of the emulsifier
• The required pH for emulsification
• The relative balance of hydrophilic and lipophilic groups
• The molecular weight of the emulsifier

Correct Answer: The relative balance of hydrophilic and lipophilic groups

Q4. Which HLB range is generally preferred for oil-in-water (O/W) emulsions?

• 3–6
• 8–18
• 15–20
• 0–3

Correct Answer: 8–18

Q5. Which mechanism primarily reduces interfacial tension during emulsification?

• Increasing temperature only
• Addition of surfactants that orient at the interface
• Applying magnetic fields
• Removing water from the system

Correct Answer: Addition of surfactants that orient at the interface

Q6. DLVO theory in colloid science explains emulsion stability by combining which two forces?

• Hydrogen bonding and Van der Waals
• Electrostatic repulsion and Van der Waals attraction
• Steric stabilization and gravitational forces
• Covalent bonding and dipole interactions

Correct Answer: Electrostatic repulsion and Van der Waals attraction

Q7. Pickering emulsions are stabilized primarily by:

• Low molecular weight surfactants only
• Solid particles adsorbed at the interface
• High electrolyte concentration
• Shear forces during homogenization

Correct Answer: Solid particles adsorbed at the interface

Q8. Which process describes phase inversion in emulsions?

• Conversion of a microemulsion into a macroemulsion
• Switching of continuous and dispersed phases (O/W to W/O or vice versa)
• Complete dehydration of the emulsion
• Transformation of an emulsion to a suspension

Correct Answer: Switching of continuous and dispersed phases (O/W to W/O or vice versa)

Q9. Spontaneous emulsification typically occurs when:

• High shear homogenization is applied
• Interfacial tension increases dramatically
• Interfacial tension decreases and a solubilization-driven mechanism takes place
• Solid particles bridge droplets

Correct Answer: Interfacial tension decreases and a solubilization-driven mechanism takes place

Q10. Which instability phenomenon is characterized by upward movement of droplets due to density differences?

• Coalescence
• Flocculation
• Creaming
• Ostwald ripening

Correct Answer: Creaming

Q11. Ostwald ripening in emulsions is driven by:

• Coalescence of equal-sized droplets only
• Diffusion of dispersed-phase molecules from smaller to larger droplets
• Electrostatic repulsion preventing coalescence
• Temperature-induced phase inversion

Correct Answer: Diffusion of dispersed-phase molecules from smaller to larger droplets

Q12. Steric stabilization is mainly provided by:

• Low molecular weight ionic surfactants
• Nonionic polymers or surfactants adsorbed at the interface
• Electrolyte addition to neutralize charge
• Increasing interfacial tension

Correct Answer: Nonionic polymers or surfactants adsorbed at the interface

Q13. Which analytical method is commonly used to determine droplet size distribution of emulsions?

• pH titration
• Laser diffraction or dynamic light scattering
• Thin layer chromatography
• UV-visible spectroscopy of bulk phase only

Correct Answer: Laser diffraction or dynamic light scattering

Q14. Microemulsions differ from macroemulsions in that microemulsions are:

• Thermodynamically unstable and require shear
• Thermodynamically stable, clear, and nanometer-sized
• Always oil-in-water with droplet size >1 μm
• Stabilized only by solid particles

Correct Answer: Thermodynamically stable, clear, and nanometer-sized

Q15. Emulsifiers that are ionic can impart stability by:

• Producing a steric barrier only
• Creating electrostatic repulsion between droplets
• Increasing droplet coalescence
• Reducing continuous phase viscosity only

Correct Answer: Creating electrostatic repulsion between droplets

Q16. What is the primary role of co-surfactants in microemulsion formation?

• To increase droplet density
• To further reduce interfacial tension and fluidize the interfacial film
• To act as preservatives
• To increase the molecular weight of emulsifier

Correct Answer: To further reduce interfacial tension and fluidize the interfacial film

Q17. Which of the following is NOT a common pharmaceutical emulsifying agent?

• Sodium lauryl sulfate
• Sorbitan esters (Spans)
• Polysorbates (Tweens)
• Cellulose acetate (as a primary surfactant)

Correct Answer: Cellulose acetate (as a primary surfactant)

Q18. The required HLB (rHLB) of an oil is defined as:

• The HLB of the oil phase itself
• The HLB of the surfactant blend needed to form a stable emulsion with that oil
• The optimum pH for emulsification
• The temperature at which phase inversion occurs

Correct Answer: The HLB of the surfactant blend needed to form a stable emulsion with that oil

Q19. In a W/O emulsion, which statement is true?

• The continuous phase is water and droplets are oil
• The continuous phase is oil and droplets are water
• Both phases are completely miscible
• It is always transparent

Correct Answer: The continuous phase is oil and droplets are water

Q20. Zeta potential measurement helps to predict emulsion stability by indicating:

• The molecular weight distribution of surfactant
• The degree of electrostatic repulsion between droplets
• The exact droplet size in nm
• The amount of co-surfactant needed

Correct Answer: The degree of electrostatic repulsion between droplets

Q21. Which factor generally decreases emulsion stability?

• Increasing continuous phase viscosity
• Matching emulsifier HLB with oil rHLB
• Presence of electrolytes causing charge neutralization
• Use of steric stabilizers

Correct Answer: Presence of electrolytes causing charge neutralization

Q22. Coalescence in an emulsion refers to:

• Small droplets aggregating without merging
• Droplets merging to form larger droplets
• Solute crystallization in the dispersed phase
• Droplet diffusion from larger to smaller ones

Correct Answer: Droplets merging to form larger droplets

Q23. Which equipment is most suitable for producing very small droplet emulsions (nanoemulsions) in pharmaceuticals?

• Simple paddle mixer
• High-pressure homogenizer or ultrasonic homogenizer
• Magnetic stirrer at low rpm
• Mortar and pestle

Correct Answer: High-pressure homogenizer or ultrasonic homogenizer

Q24. Bancroft’s rule has limitations; one limitation is:

• It always predicts microemulsion formation accurately
• It ignores the effects of surfactant concentration and temperature
• It only applies to emulsions stabilized by solid particles
• It is valid only for ionic surfactants at high pH

Correct Answer: It ignores the effects of surfactant concentration and temperature

Q25. Which phrase best defines a multiple emulsion?

• An emulsion stabilized by ionic surfactants only
• A droplet-in-droplet system such as W/O/W or O/W/O
• An emulsion with particles at the interface
• An emulsion that spontaneously separates on standing

Correct Answer: A droplet-in-droplet system such as W/O/W or O/W/O

Q26. What is the primary cause of creaming that does not necessarily lead to coalescence?

• Brownian motion dominating gravitational forces
• Density differences between dispersed and continuous phases
• Complete miscibility of phases
• Surfactant-induced flocculation

Correct Answer: Density differences between dispersed and continuous phases

Q27. Which effect does increasing temperature commonly have on nonionic surfactant-stabilized emulsions?

• It always increases stability irrespective of temperature
• It may cause phase inversion at the phase inversion temperature (PIT)
• It converts emulsifiers to solids
• It has no effect on HLB

Correct Answer: It may cause phase inversion at the phase inversion temperature (PIT)

Q28. Which surfactant type would you choose to stabilize an oil-in-water emulsion of a highly polar oil?

• Low HLB nonionic surfactant
• High HLB hydrophilic surfactant
• No surfactant is needed for polar oils
• Strongly lipophilic surfactant only

Correct Answer: High HLB hydrophilic surfactant

Q29. Which parameter is most directly linked to the rate of Ostwald ripening?

• Viscosity of the continuous phase only
• Solubility of dispersed phase in continuous phase
• pH of the continuous phase
• Color of the emulsion

Correct Answer: Solubility of dispersed phase in continuous phase

Q30. Which of the following best describes the role of emulsifying agents in preventing coalescence?

• They increase interfacial tension to prevent merging
• They form a protective film around droplets reducing interfacial energy
• They cause droplets to become heavier so they sediment
• They chemically react with the dispersed phase to solidify droplets

Correct Answer: They form a protective film around droplets reducing interfacial energy

Q31. The term “interfacial film rigidity” affects emulsion stability by:

• Making droplets more prone to coalescence when the film is rigid
• Preventing coalescence when the film is sufficiently flexible and viscoelastic
• Having no influence on droplet interactions
• Always destabilizing Pickering emulsions only

Correct Answer: Preventing coalescence when the film is sufficiently flexible and viscoelastic

Q32. Which property is increased by adding a thickening agent to the continuous phase of an emulsion?

• Rate of Ostwald ripening
• Interfacial tension between phases
• Overall emulsion viscosity and resistance to creaming
• Volatility of the dispersed phase

Correct Answer: Overall emulsion viscosity and resistance to creaming

Q33. In the context of emulsions, “coacervation” refers to:

• Formation of a polymer-rich phase around droplets leading to stabilization or encapsulation
• Emulsion droplets undergoing phase inversion
• Complete dissolution of dispersed phase into continuous phase
• Crystallization of the emulsifier

Correct Answer: Formation of a polymer-rich phase around droplets leading to stabilization or encapsulation

Q34. Which indicator test can quickly distinguish O/W from W/O emulsions?

• Drop test with dye-soluble only in continuous phase (e.g., water-soluble dye)
• Measuring droplet density with centrifugation only
• Measuring zeta potential exclusively
• Observing color change under UV light

Correct Answer: Drop test with dye-soluble only in continuous phase (e.g., water-soluble dye)

Q35. Which of the following surfactants is nonionic?

• Sodium dodecyl sulfate (SDS)
• Polysorbate 80 (Tween 80)
• Cetyltrimethylammonium bromide (CTAB)
• Sodium lauryl ether sulfate (SLES)

Correct Answer: Polysorbate 80 (Tween 80)

Q36. Which parameter is least likely to be influenced by the choice of emulsifier?

• Type of emulsion (O/W or W/O)
• Rate of coalescence
• Color of the oil phase chemical structure
• Interfacial film properties

Correct Answer: Color of the oil phase chemical structure

Q37. Which statement about Pickering emulsions is correct?

• They are stabilized exclusively by ionic surfactants
• They can show very high stability due to irreversibly adsorbed particles
• They always require high HLB surfactants
• They are thermodynamically stable like microemulsions

Correct Answer: They can show very high stability due to irreversibly adsorbed particles

Q38. The phase inversion temperature (PIT) method exploits which property of nonionic surfactants?

• pH sensitivity
• Temperature-dependent hydration causing changes in HLB-like behavior
• Magnetic susceptibility changes
• Light-scattering ability

Correct Answer: Temperature-dependent hydration causing changes in HLB-like behavior

Q39. Which of the following reduces Ostwald ripening in an emulsion?

• Using a dispersed phase with high solubility in the continuous phase
• Adding a second oil with very low solubility (osmotic stabilizer)
• Decreasing continuous-phase viscosity only
• Increasing temperature drastically

Correct Answer: Adding a second oil with very low solubility (osmotic stabilizer)

Q40. Which observation indicates flocculation rather than coalescence?

• Droplets merge to form larger single spherical droplets
• An emulsion becomes a single continuous phase
• Formation of clusters of droplets that remain distinct and can be redispersed
• Complete dissolution of droplets into the continuous phase

Correct Answer: Formation of clusters of droplets that remain distinct and can be redispersed

Q41. In designing an O/W topical emulsion, which surfactant system is typically preferred for skin compatibility?

• Strong anionic surfactants like SDS in high concentration
• Mild nonionic surfactants such as polysorbates and poloxamers
• High concentrations of cationic quats only
• No surfactant for better spreadability

Correct Answer: Mild nonionic surfactants such as polysorbates and poloxamers

Q42. What is the expected effect of adding electrolytes to an emulsion stabilized by ionic surfactants?

• Increase electrostatic repulsion and stabilize indefinitely
• Compress the electrical double layer and may cause flocculation or coalescence
• Convert the emulsion to a microemulsion always
• Have no effect on stability

Correct Answer: Compress the electrical double layer and may cause flocculation or coalescence

Q43. Which property of an emulsifier blend would you adjust to match the required HLB of an oil?

• The pH of the blend only
• The ratio of low to high HLB surfactants in the blend
• The color and odor of the blend
• The molecular weight distribution exclusively

Correct Answer: The ratio of low to high HLB surfactants in the blend

Q44. Which measurement provides information about droplet surface charge in emulsions?

• Differential scanning calorimetry (DSC)
• Zeta potential measurement
• Thermogravimetric analysis (TGA)
• Refractometry of the continuous phase

Correct Answer: Zeta potential measurement

Q45. Which approach is commonly used to prepare W/O/W multiple emulsions in pharmaceuticals?

• Simple dilution of W/O emulsions without stabilizers
• Two-step emulsification using appropriate internal and external emulsifiers
• Dry milling of surfactants with oil only
• Adding electrolytes to destabilize primary emulsion

Correct Answer: Two-step emulsification using appropriate internal and external emulsifiers

Q46. Which factor most strongly influences interfacial tension between oil and water?

• Surface activity and concentration of surfactant at the interface
• Magnetic field strength
• Color of the oil
• Type of glassware used

Correct Answer: Surface activity and concentration of surfactant at the interface

Q47. Emulsions intended for parenteral administration generally require:

• High levels of microbial contamination to promote stability
• Stringent sterility, small droplet size, and use of acceptable excipients
• No emulsifier to avoid reactions
• Large droplet size (>10 μm) for easier filtration

Correct Answer: Stringent sterility, small droplet size, and use of acceptable excipients

Q48. Which effect would increasing surfactant concentration beyond the critical micelle concentration (CMC) typically have on emulsion droplet size?

• Always increase droplet size dramatically
• Often reduce droplet size up to an optimum, further increase may have limited effect
• Convert the emulsion into a crystalline solid
• Eliminate the need for co-surfactants entirely

Correct Answer: Often reduce droplet size up to an optimum, further increase may have limited effect

Q49. What role does interfacial rheology play in emulsion stability?

• It describes the flow and deformation behavior of the interfacial film, affecting resistance to rupture
• It only affects the color of the emulsion
• It determines the pH of the continuous phase exclusively
• It is irrelevant for pharmaceutical emulsions

Correct Answer: It describes the flow and deformation behavior of the interfacial film, affecting resistance to rupture

Q50. Which combination is most effective to prevent creaming and coalescence in an O/W emulsion?

• Low continuous-phase viscosity and no emulsifier
• Appropriate surfactant (correct HLB), increased continuous-phase viscosity, and small droplet size
• High dispersed phase solubility in continuous phase only
• Eliminating surfactant and relying on gravity

Correct Answer: Appropriate surfactant (correct HLB), increased continuous-phase viscosity, and small droplet size

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