Emulsions – definition and classification MCQs With Answer

Emulsions are biphasic dispersed systems where one immiscible liquid is dispersed as droplets in another, stabilized by emulsifying agents. For B. Pharm students, mastering the definition and classification of emulsions—o/w (oil-in-water), w/o (water-in-oil), multiple emulsions (w/o/w, o/w/o), microemulsions, and nanoemulsions—is essential. Key formulation concepts include HLB, Bancroft rule, surfactant types (anionic, cationic, nonionic, natural, and Pickering), droplet size, phase volume ratio, and interfacial film. Identification tests (dye, conductivity, dilution, cobalt chloride) and stability concerns (creaming, flocculation, coalescence, cracking) governed by Stokes’ law guide selection and optimization. Preparation methods (dry gum, wet gum, Forbes bottle, PIT) help control phase inversion and performance in oral, topical, and parenteral dosage forms. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which statement best defines an emulsion in pharmaceutics?

• A homogeneous solution of two miscible liquids
• A biphasic system of two immiscible liquids with one dispersed as droplets in the other
• A suspension of solid particles in a liquid medium
• A gel network entrapping aqueous phase only

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

Q2. Emulsion classification into o/w and w/o is primarily based on which parameter?

• Type of drug dissolved
• The viscosity of the preparation
• The identity of the continuous (external) phase
• The manufacturing equipment used

Correct Answer: The identity of the continuous (external) phase

Q3. In a w/o emulsion, which statement is correct?

• Oil droplets are dispersed in a continuous water phase
• Water droplets are dispersed in a continuous oil phase
• Both phases form a bicontinuous network at all times
• Neither phase is continuous

Correct Answer: Water droplets are dispersed in a continuous oil phase

Q4. Milk is an example of which type of emulsion?

• Water-in-oil (w/o)
• Oil-in-water (o/w)
• Multiple w/o/w
• Microemulsion

Correct Answer: Oil-in-water (o/w)

Q5. Which description correctly defines a w/o/w multiple emulsion?

• Oil droplets dispersed in oil
• Water droplets dispersed in water
• Water droplets inside oil droplets, further dispersed in an external water phase
• Oil droplets inside water droplets, further dispersed in an external oil phase

Correct Answer: Water droplets inside oil droplets, further dispersed in an external water phase

Q6. Which characteristic distinguishes microemulsions from conventional emulsions?

• They are thermodynamically stable and often transparent
• They require no surfactants to form
• They always have droplet sizes >10 µm
• They are always w/o systems

Correct Answer: They are thermodynamically stable and often transparent

Q7. Typical droplet size range for nanoemulsions is:

• 1–10 nm
• 20–200 nm
• 2–10 µm
• 10–100 µm

Correct Answer: 20–200 nm

Q8. Bancroft’s rule states that the external phase of an emulsion is determined mainly by:

• The drug’s partition coefficient
• The phase with the larger volume
• The phase in which the emulsifier is more soluble
• The mixing speed during emulsification

Correct Answer: The phase in which the emulsifier is more soluble

Q9. Surfactants with which HLB range generally favor formation of o/w emulsions?

• 3–6
• 6–8
• 8–18
• 18–25

Correct Answer: 8–18

Q10. Which emulsifier most commonly favors o/w emulsions?

• Sorbitan monooleate (Span 80)
• Polysorbate 80 (Tween 80)
• Aluminum stearate
• Beeswax

Correct Answer: Polysorbate 80 (Tween 80)

Q11. Which emulsifier most commonly favors w/o emulsions?

• Polysorbate 20 (Tween 20)
• Sodium lauryl sulfate
• Sorbitan monooleate (Span 80)
• Gelatin

Correct Answer: Sorbitan monooleate (Span 80)

Q12. In the dye solubility test, a water-soluble dye uniformly colors the continuous phase. What does this indicate?

• The emulsion is w/o
• The emulsion is o/w
• The emulsion is multiple
• The emulsion is microemulsion

Correct Answer: The emulsion is o/w

Q13. Which emulsion type typically shows higher electrical conductivity?

• Oil-in-water (o/w)
• Water-in-oil (w/o)
• Multiple w/o/w
• Both o/w and w/o conduct equally

Correct Answer: Oil-in-water (o/w)

Q14. The dilution test for emulsion type is based on:

• Compatibility with the internal phase
• Compatibility with the external phase
• Ability to dissolve dyes
• Ability to foam upon shaking

Correct Answer: Compatibility with the external phase

Q15. In the cobalt chloride paper test, which outcome indicates an o/w emulsion?

• Paper changes from blue to pink quickly upon contact
• Paper remains blue even after rubbing
• Paper turns black rapidly
• Paper becomes oily but unchanged in color

Correct Answer: Paper changes from blue to pink quickly upon contact

Q16. Which statement correctly differentiates creaming from cracking?

• Creaming is irreversible; cracking is reversible
• Both are irreversible instabilities
• Creaming is reversible separation by density difference; cracking is irreversible phase separation
• Both are prevented by reducing droplet size to >10 µm

Correct Answer: Creaming is reversible separation by density difference; cracking is irreversible phase separation

Q17. According to Stokes’ law, which change will reduce the rate of creaming?

• Increase droplet diameter
• Increase density difference between phases
• Decrease continuous phase viscosity
• Increase continuous phase viscosity

Correct Answer: Increase continuous phase viscosity

Q18. Which factor directly increases creaming velocity in an emulsion?

• Smaller droplet size
• Larger droplet size (diameter squared dependence)
• Lower density difference between phases
• Higher continuous phase viscosity

Correct Answer: Larger droplet size (diameter squared dependence)

Q19. Which change can trigger phase inversion in emulsions?

• Reducing interfacial tension
• Increasing internal phase volume fraction beyond a critical limit
• Adding a preservative
• Decreasing temperature slightly in all systems

Correct Answer: Increasing internal phase volume fraction beyond a critical limit

Q20. The Phase Inversion Temperature (PIT) method relies on what property of nonionic surfactants?

• Increased hydrophilicity with rising temperature due to more hydration
• Decreased hydrophilicity with rising temperature due to dehydration of ethoxy groups
• Charge reversal with temperature change
• Complete insolubility in both phases at high temperature

Correct Answer: Decreased hydrophilicity with rising temperature due to dehydration of ethoxy groups

Q21. In the continental (dry gum) method for fixed oil emulsions, the typical oil:water:gum ratio is:

• 2:4:1
• 4:2:1
• 3:2:1
• 1:2:4

Correct Answer: 4:2:1

Q22. In the English (wet gum) method, which order is correct?

• Oil and gum triturated first; then water added all at once
• Gum and water triturated first to mucilage; then oil added gradually
• Oil and water shaken in bottle; gum added at the end
• Water added to oil while heating; gum added after cooling

Correct Answer: Gum and water triturated first to mucilage; then oil added gradually

Q23. The Forbes bottle method is particularly suitable for emulsifying:

• Fixed (nonvolatile) oils only
• Volatile and essential oils prone to foaming
• Aqueous solutions with high electrolytes
• Solid-in-liquid suspensions

Correct Answer: Volatile and essential oils prone to foaming

Q24. Which is a correct pairing of emulsifier class and example?

• Anionic – Benzalkonium chloride
• Cationic – Sodium lauryl sulfate
• Nonionic – Polysorbate 80 (Tween 80)
• Natural – Cetyltrimethylammonium bromide

Correct Answer: Nonionic – Polysorbate 80 (Tween 80)

Q25. Pickering emulsions are stabilized primarily by:

• High concentrations of alcohol co-solvents
• Solid particles adsorbed at the interface
• Electrolyte-induced micellization
• Protein denaturation

Correct Answer: Solid particles adsorbed at the interface

Q26. Which is a key pharmaceutical application of multiple (w/o/w) emulsions?

• Immediate increase in drug dissolution rate
• Sustained/controlled release and protection of labile drugs
• Reducing viscosity of topical formulations
• Improving taste of sweet solutions only

Correct Answer: Sustained/controlled release and protection of labile drugs

Q27. In Winsor phase behavior, which system describes a single, homogeneous microemulsion phase?

• Winsor I
• Winsor II
• Winsor III
• Winsor IV

Correct Answer: Winsor IV

Q28. For intravenous administration, emulsions must be:

• Water-in-oil (w/o) to match plasma lipids
• Oil-in-water (o/w) to be compatible with blood
• Multiple w/o/w for sustained effect
• Pickering type stabilized by silica

Correct Answer: Oil-in-water (o/w) to be compatible with blood

Q29. Which emulsion type is preferred for occlusive, moisturizing skin creams?

• Oil-in-water (o/w) because it is easily washable
• Water-in-oil (w/o) because it reduces transepidermal water loss
• Multiple o/w/o because it is nonocclusive
• Microemulsions because they are always occlusive

Correct Answer: Water-in-oil (w/o) because it reduces transepidermal water loss

Q30. The required HLB of an oil blend for o/w emulsification is calculated as:

• The arithmetic mean of the surfactant HLB values
• The weighted average of the components’ required HLB values based on their proportions
• The highest required HLB among all oils in the blend
• The geometric mean of oil densities

Correct Answer: The weighted average of the components’ required HLB values based on their proportions

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