Emulsifying agents MCQs With Answer

Emulsifying agents are key excipients in pharmaceutics, enabling stable emulsions by reducing interfacial tension, forming protective interfacial films, and providing electrostatic or steric stabilization. B. Pharm students must master classification (anionic, cationic, nonionic, natural), HLB system, selection of O/W vs W/O emulsifiers, Bancroft’s rule, and formulation methods (dry gum, wet gum, bottle method). Typical emulsifiers include acacia, lecithin, polysorbates (Tween), and sorbitan esters (Span), used with co-emulsifiers and viscosity enhancers to combat creaming, coalescence, cracking, and phase inversion. Understanding tests (dye, conductivity, dilution), microemulsions, required HLB, and parenteral constraints ensures safe, effective dosage forms in pharmaceutical technology. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary function of an emulsifying agent in pharmaceutical emulsions?

• Substances that reduce interfacial tension and stabilize droplets in emulsions
• Agents that increase viscosity only without adsorbing at interfaces
• Compounds that dissolve both liquids completely
• Electrolytes used to adjust pH

Correct Answer: Substances that reduce interfacial tension and stabilize droplets in emulsions

Q2. Which statement best describes the HLB (Hydrophilic–Lipophilic Balance) concept?

• An empirical scale expressing the balance of hydrophilic and lipophilic portions in nonionic surfactants
• A scale quantifying only the viscosity of emulsifiers
• A measure of droplet size distribution in emulsions
• An index of preservative potency in O/W systems

Correct Answer: An empirical scale expressing the balance of hydrophilic and lipophilic portions in nonionic surfactants

Q3. The typical HLB scale used for nonionic surfactants ranges from:

• 0–20
• 1–100
• 0–1
• 100–1000

Correct Answer: 0–20

Q4. Which HLB range is commonly preferred to form oil-in-water (O/W) emulsions?

• 8–18
• 3–6
• 20–40
• 0–2

Correct Answer: 8–18

Q5. Which of the following is a typical O/W emulsifier used in pharmaceuticals?

• Polysorbate 80 (Tween 80)
• Sorbitan monooleate (Span 80)
• Cholesterol
• Sorbitan monostearate (Span 60)

Correct Answer: Polysorbate 80 (Tween 80)

Q6. Which emulsifier is best suited for forming W/O emulsions?

• Sorbitan monooleate (Span 80)
• Sodium lauryl sulfate
• Polysorbate 20 (Tween 20)
• Acacia (gum arabic)

Correct Answer: Sorbitan monooleate (Span 80)

Q7. Bancroft’s rule states that the external phase of an emulsion is determined by the phase in which the emulsifier is:

• More soluble
• Less soluble
• Equally distributed
• Insoluble

Correct Answer: More soluble

Q8. Acacia (gum arabic) is primarily used to prepare which type of emulsion?

• Oil-in-water (O/W) emulsion
• Water-in-oil (W/O) emulsion
• Microemulsion
• Multiple emulsion (W/O/W)

Correct Answer: Oil-in-water (O/W) emulsion

Q9. In the continental (dry gum) method with acacia and a fixed oil, the standard primary emulsion ratio (oil:water:gum) is:

• 4:2:1
• 2:2:1
• 1:2:4
• 3:2:1

Correct Answer: 4:2:1

Q10. Which test result most strongly indicates an O/W emulsion?

• High electrical conductivity due to a continuous water phase
• Uniform staining by oil-soluble dye
• Inability to dilute with water
• Strong fluorescence under UV due to continuous oil phase

Correct Answer: High electrical conductivity due to a continuous water phase

Q11. If an oil-soluble dye (e.g., Sudan III) uniformly stains the external phase of an emulsion, the emulsion type is likely:

• W/O emulsion
• O/W emulsion
• Multiple emulsion
• Microemulsion

Correct Answer: W/O emulsion

Q12. Benzalkonium chloride (a cationic surfactant) is incompatible with which class of emulsifiers?

• Anionic surfactants (e.g., sodium lauryl sulfate)
• Nonionic surfactants (e.g., polysorbates)
• Amphoteric surfactants (e.g., lecithin)
• Co-solvents (e.g., propylene glycol)

Correct Answer: Anionic surfactants (e.g., sodium lauryl sulfate)

Q13. Nonionic emulsifiers like polysorbates primarily stabilize emulsions by:

• Steric hindrance at the interface
• Strong electrostatic repulsion
• Chemical crosslinking of droplets
• pH buffering

Correct Answer: Steric hindrance at the interface

Q14. Which statement about microemulsions is most accurate?

• They are thermodynamically stable and require a co-surfactant
• They are always opaque due to large droplet size
• They are less stable than coarse emulsions
• They cannot solubilize lipophilic drugs

Correct Answer: They are thermodynamically stable and require a co-surfactant

Q15. According to Stokes’ law, which change most effectively reduces creaming in an emulsion?

• Decreasing droplet size by efficient homogenization
• Increasing temperature of storage
• Using a lower viscosity continuous phase
• Increasing droplet density relative to the medium

Correct Answer: Decreasing droplet size by efficient homogenization

Q16. The irreversible separation of phases in an emulsion is termed:

• Cracking (breaking)
• Creaming
• Flocculation
• Sedimentation

Correct Answer: Cracking (breaking)

Q17. Which factor commonly triggers phase inversion in nonionic surfactant-stabilized systems?

• Temperature change near the phase inversion temperature (PIT)
• Removal of all electrolytes
• Addition of a water-miscible cosolvent
• Increase in headspace air

Correct Answer: Temperature change near the phase inversion temperature (PIT)

Q18. For parenteral O/W emulsions (e.g., intravenous nutrition), a preferred emulsifier is:

• Egg lecithin (phospholipids)
• Sodium lauryl sulfate
• Benzalkonium chloride
• Sorbitan monooleate (Span 80)

Correct Answer: Egg lecithin (phospholipids)

Q19. How is the HLB of a surfactant blend typically calculated?

• Weighted average based on the weight fraction of each surfactant
• Simple arithmetic mean ignoring proportions
• Geometric mean of HLB values
• By matching the cloud point

Correct Answer: Weighted average based on the weight fraction of each surfactant

Q20. Cetyl alcohol in creams primarily functions as a:

• Co-emulsifier and stabilizer that strengthens the interfacial film and increases viscosity
• Primary anionic emulsifier for O/W systems
• Preservative against microbial growth
• Humectant that decreases water activity

Correct Answer: Co-emulsifier and stabilizer that strengthens the interfacial film and increases viscosity

Q21. In the dilution test, an emulsion that can be diluted only with oil (but not with water) is:

• A W/O emulsion
• An O/W emulsion
• A microemulsion
• A multiple emulsion

Correct Answer: A W/O emulsion

Q22. Calcium soaps (e.g., calcium palmitate) typically form which type of emulsion?

• W/O emulsions
• O/W emulsions
• Microemulsions
• W/O/W multiple emulsions

Correct Answer: W/O emulsions

Q23. O/W emulsions stabilized by anionic emulsifiers generally have droplets with which surface charge?

• Negative
• Positive
• Neutral
• Variable but independent of emulsifier

Correct Answer: Negative

Q24. Why are preservatives particularly important in acacia-based O/W emulsions?

• Because the aqueous phase and natural gum favor microbial growth
• Because oil phase always sterilizes the product
• Because emulsifiers deactivate drug activity
• Because O/W emulsions cannot be refrigerated

Correct Answer: Because the aqueous phase and natural gum favor microbial growth

Q25. In the PIT method for preparing O/W emulsions with ethoxylated nonionic surfactants, optimal stability is achieved by:

• Cooling the system well below the PIT after homogenization
• Heating and storing above the PIT
• Adding strong electrolytes to raise the PIT
• Eliminating co-surfactants

Correct Answer: Cooling the system well below the PIT after homogenization

Q26. The approximate required HLB of mineral oil for O/W emulsification is:

• About 10–12
• 3–6
• 4–6
• 15–18

Correct Answer: About 10–12

Q27. Which of the following is a nonionic emulsifier?

• Polysorbate 20 (Tween 20)
• Sodium dodecyl sulfate (SDS)
• Benzalkonium chloride
• Sodium stearate

Correct Answer: Polysorbate 20 (Tween 20)

Q28. A practical strategy to reduce Ostwald ripening in nanoemulsions is to:

• Incorporate a small amount of highly insoluble oil (e.g., squalene)
• Increase the temperature during storage
• Use only ionic surfactants
• Decrease continuous phase viscosity

Correct Answer: Incorporate a small amount of highly insoluble oil (e.g., squalene)

Q29. If the emulsifier concentration is below the critical level needed for coverage of droplets, the most likely outcome is:

• Coalescence leading to breaking
• Increased shelf-life
• Formation of microemulsion spontaneously
• Complete prevention of creaming

Correct Answer: Coalescence leading to breaking

Q30. In topical creams, emulsifying agents are primarily used to:

• Stabilize dispersed phases, improve texture, and enhance spreadability
• Increase drug potency through chemical reaction
• Replace preservatives entirely
• Decrease drug solubility

Correct Answer: Stabilize dispersed phases, improve texture, and enhance spreadability

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