Pharmaceutical dispersions: emulsions MCQs With Answer

Pharmaceutical dispersions: emulsions MCQs With Answer are designed to help M.Pharm students master advanced concepts in Modern Pharmaceutics (MPH 103T). Emulsions play a critical role in oral, topical and parenteral dosage forms, and their successful design demands a sound grasp of interfacial phenomena, surfactant science, stability mechanisms, processing, and regulatory quality attributes. This set of questions goes beyond basics to test understanding of HLB systems, Bancroft’s rule, phase inversion, droplet size analysis, rheology, and instability pathways like creaming, coalescence and Ostwald ripening. You will also find clinically relevant aspects such as USP <729> specifications for intravenous lipid emulsions and practical formulation strategies including emulsifier blending and preservative selection. Review the explanations by verifying the correct options provided after each question.

Q1. According to Bancroft’s rule, which factor primarily determines the continuous phase of an emulsion?

• The phase present in larger volume at the end of emulsification
• The phase in which the emulsifier is more soluble
• The phase with higher viscosity
• The phase with higher density

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

Q2. Which statement best distinguishes microemulsions from nanoemulsions?

• Microemulsions are kinetically stable and require low surfactant; nanoemulsions are thermodynamically stable
• Microemulsions are thermodynamically stable and typically 10–100 nm; nanoemulsions are kinetically stable and typically 20–200 nm
• Both are thermodynamically stable dispersions
• Both require cosurfactants in all cases to be stable

Correct Answer: Microemulsions are thermodynamically stable and typically 10–100 nm; nanoemulsions are kinetically stable and typically 20–200 nm

Q3. Based on Stokes’ law, which change will increase the creaming velocity in an O/W emulsion?

• Decreasing droplet radius
• Increasing continuous-phase viscosity
• Decreasing density difference between phases
• Increasing droplet radius

Correct Answer: Increasing droplet radius

Q4. The most effective strategy to suppress Ostwald ripening in an oil-in-water nanoemulsion is to:

• Increase the emulsifier HLB beyond 18
• Add a small amount of a highly insoluble oil (ripening inhibitor) to the dispersed oil
• Use a cationic surfactant instead of a nonionic surfactant
• Decrease processing temperature during homogenization

Correct Answer: Add a small amount of a highly insoluble oil (ripening inhibitor) to the dispersed oil

Q5. Typical required HLB ranges for stable emulsions are:

• O/W: 3–6; W/O: 8–18
• O/W: 8–18; W/O: 3–6
• O/W: 1–3; W/O: 13–18
• O/W: 6–10; W/O: 10–14

Correct Answer: O/W: 8–18; W/O: 3–6

Q6. For nonionic surfactants, Griffin’s HLB is calculated using which expression?

• HLB = 7 + Σ(hydrophilic group numbers) − Σ(lipophilic group numbers)
• HLB = 20 × (Mh/M)
• HLB = 10 × log P
• HLB = 1/(CMC)

Correct Answer: HLB = 20 × (Mh/M)

Q7. Which statement about the Davies method for estimating HLB is correct?

• It is applicable only to nonionic surfactants
• It uses a polymeric cloud point to compute HLB
• It uses group numbers to estimate HLB and is applicable to ionic and nonionic surfactants
• It gives the same HLB as Griffin’s method for all surfactants

Correct Answer: It uses group numbers to estimate HLB and is applicable to ionic and nonionic surfactants

Q8. Regarding Phase Inversion Temperature (PIT) in emulsions stabilized by ethoxylated nonionic surfactants, which is most accurate?

• At PIT, the emulsion is most stable and coalescence is minimized
• Cooling rapidly from slightly above PIT can yield very small droplets
• Heating far above PIT prevents inversion
• PIT is unaffected by electrolyte or oil type

Correct Answer: Cooling rapidly from slightly above PIT can yield very small droplets

Q9. Which combination reflects USP <729> quality attributes for intravenous lipid emulsions?

• Mean droplet diameter ≤ 500 nm and PFAT5 ≤ 0.05%
• Mean droplet diameter ≤ 1000 nm and PFAT5 ≤ 0.5%
• Zeta potential ≥ ±50 mV and PFAT5 ≤ 0.05%
• Polydispersity index ≤ 0.8 and mean droplet diameter ≤ 100 nm

Correct Answer: Mean droplet diameter ≤ 500 nm and PFAT5 ≤ 0.05%

Q10. The most appropriate technique to determine the z-average droplet diameter of a 30–150 nm nanoemulsion is:

• Laser diffraction
• Optical microscopy with hemocytometer
• Dynamic light scattering (photon correlation spectroscopy)
• Sieve analysis

Correct Answer: Dynamic light scattering (photon correlation spectroscopy)

Q11. Which instrument is commonly used to measure oil–water interfacial tension during emulsifier screening?

• Du Noüy ring tensiometer
• Differential scanning calorimeter
• Polarimeter
• Brookfield viscometer

Correct Answer: Du Noüy ring tensiometer

Q12. For preparing a W/O/W multiple emulsion, a suitable emulsifier strategy is:

• Use Tween 80 to form W/O; Span 80 for the external O/W
• Use Span 80 to form W/O; Tween 80 for the external O/W
• Use only a single HLB 12 surfactant for both steps
• Use any cationic surfactant for both steps

Correct Answer: Use Span 80 to form W/O; Tween 80 for the external O/W

Q13. A common zeta potential magnitude threshold suggesting adequate electrostatic stabilization of an emulsion is approximately:

• ±5 mV
• ±15 mV
• ±30 mV
• ±60 mV

Correct Answer: ±30 mV

Q14. Which instability in emulsions is generally irreversible under normal handling?

• Creaming
• Flocculation
• Coalescence leading to cracking
• Re-dispersion upon shaking

Correct Answer: Coalescence leading to cracking

Q15. Which observation in a simple conductivity test indicates an O/W emulsion?

• Low conductivity similar to oil
• High conductivity similar to water
• No change in conductivity upon dilution with water
• Conductivity decreases upon adding electrolyte

Correct Answer: High conductivity similar to water

Q16. An oil phase requires HLB 10 for an O/W emulsion. Approximately what Tween 80:Span 80 blend (HLB 15.0 and 4.3, respectively) will achieve this?

• 70:30 Tween 80:Span 80
• 30:70 Tween 80:Span 80
• 53:47 Tween 80:Span 80
• 47:53 Tween 80:Span 80

Correct Answer: 53:47 Tween 80:Span 80

Q17. Which statement about high-pressure homogenization (HPH) versus rotor–stator mixing in emulsification is most accurate?

• Rotor–stator invariably produces smaller droplets than HPH
• HPH can achieve submicron droplets with narrower size distributions than rotor–stator mixing
• HPH is only effective for W/O emulsions
• Rotor–stator mixing prevents Ostwald ripening

Correct Answer: HPH can achieve submicron droplets with narrower size distributions than rotor–stator mixing

Q18. Concentrated, mildly flocculated O/W emulsions typically exhibit which rheological behavior?

• Newtonian flow with no yield stress
• Plastic flow with thixotropy due to a weak droplet network
• Dilatant flow with antithixotropy
• Elastic solid behavior independent of shear

Correct Answer: Plastic flow with thixotropy due to a weak droplet network

Q19. Adding electrolytes to an emulsion stabilized by an ionic surfactant most likely:

• Increases double-layer thickness and stabilizes against flocculation
• Compresses the electrical double layer, reducing zeta potential and promoting flocculation/coalescence
• Does not affect colloidal stability
• Eliminates Ostwald ripening by lowering interfacial tension

Correct Answer: Compresses the electrical double layer, reducing zeta potential and promoting flocculation/coalescence

Q20. Which approach best maintains preservative efficacy in an O/W emulsion where partitioning into oil can reduce aqueous-phase activity?

• Select a preservative with appropriate pKa/log P so that at the formulation pH sufficient preservative remains in the aqueous phase while retaining antimicrobial potency
• Always use the most lipophilic preservative available
• Increase oil content to dissolve more preservative
• Avoid adjusting pH, as it has no impact on preservative distribution

Correct Answer: Select a preservative with appropriate pKa/log P so that at the formulation pH sufficient preservative remains in the aqueous phase while retaining antimicrobial potency

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