Introduction: The formulation of emulsions is a core topic for B. Pharm students, covering principles of oil-in-water and water-in-oil systems, selection of emulsifiers, HLB concepts, droplet size control, and stability mechanisms such as creaming, coalescence, and Ostwald ripening. Practical knowledge includes preparation methods (homogenization, ultrasonication, phase inversion), role of co-surfactants, rheology modifiers, preservatives, and evaluation tests like conductivity and dilution. Understanding formulation variables directly impacts drug delivery, bioavailability, and shelf life of topical and parenteral emulsions. This focused MCQ set emphasizes both theory and applied formulation strategies to strengthen problem-solving skills. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which best defines an emulsion in pharmaceutics?
- A thermodynamically stable dispersion of two immiscible liquids
- A dispersion of one liquid phase in another immiscible liquid phase stabilized by an emulsifier
- A solid dispersed in a liquid forming a colloidal solution
- A solution where drug is molecularly dissolved in solvent
Correct Answer: A dispersion of one liquid phase in another immiscible liquid phase stabilized by an emulsifier
Q2. Which two main types of emulsions are commonly used in pharmaceutical formulations?
- Emulsion and suspension
- Ointments and creams
- Oil-in-water (O/W) and water-in-oil (W/O)
- Sublingual and buccal
Correct Answer: Oil-in-water (O/W) and water-in-oil (W/O)
Q3. What does HLB stand for and why is it important in emulsifier selection?
- High-Low Balance; indicates melting point of emulsifier
- Hydrophilic–Lipophilic Balance; predicts emulsifier affinity for oil or water phases
- Heat-Labile Bonding; measures thermal stability of surfactant
- Hydro-Lytic Breakpoint; predicts hydrolysis susceptibility
Correct Answer: Hydrophilic–Lipophilic Balance; predicts emulsifier affinity for oil or water phases
Q4. Which HLB value range is generally suitable for oil-in-water (O/W) emulsifiers?
- 1–3
- 3–6
- 8–18
- 20–30
Correct Answer: 8–18
Q5. Which mechanism is primarily responsible for creaming in emulsions?
- Chemical degradation of emulsifier
- Density difference between dispersed droplets and continuous phase causing upward or downward movement
- Complete coalescence of all droplets into a single phase
- Osmotic pressure imbalance
Correct Answer: Density difference between dispersed droplets and continuous phase causing upward or downward movement
Q6. Which process most directly reduces droplet size during emulsion manufacture?
- Freeze-thaw cycling
- High-shear homogenization or high-pressure homogenization
- Simple magnetic stirring at low rpm
- Static holding at elevated temperature
Correct Answer: High-shear homogenization or high-pressure homogenization
Q7. What role does a co-surfactant play in microemulsion formation?
- Increases interfacial tension to promote phase separation
- Acts as preservative to prevent microbial growth
- Reduces interfacial film rigidity and expands the interfacial region to stabilize microemulsions
- Converts oil into water by chemical reaction
Correct Answer: Reduces interfacial film rigidity and expands the interfacial region to stabilize microemulsions
Q8. Which test can quickly distinguish O/W from W/O emulsions?
- Viscometry test at 1000 rpm
- Conductivity test and dilution with water
- pH measurement
- Colorimetric assay
Correct Answer: Conductivity test and dilution with water
Q9. Which instability phenomenon involves irreversible merging of emulsion droplets?
- Flocculation
- Creaming
- Coalescence
- Ostwald ripening
Correct Answer: Coalescence
Q10. Ostwald ripening in emulsions is driven by:
- Gravitational forces alone
- Diffusion of dispersed phase molecules from smaller to larger droplets due to solubility differences
- Aggregation without any mass transfer
- Loss of emulsifier by volatilization
Correct Answer: Diffusion of dispersed phase molecules from smaller to larger droplets due to solubility differences
Q11. Which excipient class is commonly used to increase continuous-phase viscosity and reduce creaming?
- Preservatives
- Viscosity enhancers/thickeners (e.g., carbomers, xanthan gum)
- Antioxidants
- Buffers
Correct Answer: Viscosity enhancers/thickeners (e.g., carbomers, xanthan gum)
Q12. Which surfactant type usually produces water-in-oil (W/O) emulsions?
- Highly hydrophilic surfactants with HLB > 12
- Hydrophobic surfactants with low HLB values (e.g., 3–6)
- Non-ionic surfactants exclusively
- Any surfactant at very high concentration
Correct Answer: Hydrophobic surfactants with low HLB values (e.g., 3–6)
Q13. Which parameter is commonly used to assess emulsion droplet size distribution?
- pH meter readings
- Laser diffraction or dynamic light scattering measurements
- Refractive index only
- Color observation
Correct Answer: Laser diffraction or dynamic light scattering measurements
Q14. What is the typical droplet size range that distinguishes microemulsions from conventional emulsions?
- Microemulsions: 1–100 nm; conventional emulsions: >200 nm
- Microemulsions: 1–10 µm; conventional emulsions: 10–100 µm
- Microemulsions: >1 mm; conventional emulsions: <1 mm
- No difference in droplet size exists
Correct Answer: Microemulsions: 1–100 nm; conventional emulsions: >200 nm
Q15. Which emulsifier is an example of a non-ionic surfactant commonly used in pharmaceutical emulsions?
- Sodium lauryl sulfate
- Polysorbate 80 (Tween 80)
- Benzalkonium chloride
- Calcium stearate
Correct Answer: Polysorbate 80 (Tween 80)
Q16. Why is pH important in emulsion formulation for certain drugs?
- It determines droplet color only
- It affects drug ionization, emulsifier stability, and potential hydrolysis of labile drugs
- It prevents creaming by itself
- pH has no impact on emulsions
Correct Answer: It affects drug ionization, emulsifier stability, and potential hydrolysis of labile drugs
Q17. Which method is based on changing temperature to invert emulsion type temporarily during preparation?
- Ultrasonic emulsification
- Phase inversion temperature (PIT) method
- Solvent evaporation
- Cold chain stabilization
Correct Answer: Phase inversion temperature (PIT) method
Q18. Which evaluation indicates an O/W emulsion when performing dye solubility tests?
- Oil-soluble dye colors only the continuous phase
- Water-soluble dye disperses throughout the continuous phase indicating O/W
- Dye test is not applicable to emulsions
- Both dyes always mix uniformly regardless of type
Correct Answer: Water-soluble dye disperses throughout the continuous phase indicating O/W
Q19. Which preservative compatibility concern is critical for emulsions?
- Preservatives always partition into oil phase, so concentration is irrelevant
- Preservative efficacy can be reduced if it partitions into the oil phase or is bound by emulsifiers
- Preservatives have no interaction with emulsifiers
- Preservatives increase HLB of surfactants
Correct Answer: Preservative efficacy can be reduced if it partitions into the oil phase or is bound by emulsifiers
Q20. Which packing and container choice best protects sensitive emulsions from light and oxygen?
- Clear plastic bottles with large headspace
- Amber glass or air-tight containers with minimal headspace
- Open jars stored at room temperature
- Thin-walled metal cans without liners
Correct Answer: Amber glass or air-tight containers with minimal headspace
Q21. Which rheological property is often targeted to improve spreadability yet reduce phase separation in topical emulsions?
- High Newtonian viscosity only
- Shear-thinning (pseudoplastic) behavior with appropriate yield value
- Bingham plastic behavior with no yield stress
- Viscosity that increases with shear rate (dilatant)
Correct Answer: Shear-thinning (pseudoplastic) behavior with appropriate yield value
Q22. Electrical conductivity of an emulsion is highest when:
- The continuous phase is oil
- The continuous phase is water (O/W emulsion)
- No continuous phase exists
- Emulsifier concentration is zero
Correct Answer: The continuous phase is water (O/W emulsion)
Q23. Which factor most directly lowers interfacial tension between oil and water during emulsification?
- Adding non-solvent
- Adding surfactant/emulsifier to the interface
- Cooling the mixture below freezing
- Increasing particle size of oil droplets
Correct Answer: Adding surfactant/emulsifier to the interface
Q24. Which is a common method to sterilize parenteral emulsions without damaging the emulsion?
- Autoclaving at high temperature for long durations
- Sterile filtration is often not feasible; instead, aseptic manufacturing with terminal sterilization by filtration of components and aseptic filling
- Addition of strong acids to kill microbes
- Exposing to direct sunlight
Correct Answer: Sterile filtration is often not feasible; instead, aseptic manufacturing with terminal sterilization by filtration of components and aseptic filling
Q25. What is multiple (W/O/W or O/W/O) emulsion useful for in drug delivery?
- To provide immediate drug release only
- To encapsulate drugs for controlled release or protect unstable drugs from the external phase
- To reduce viscosity for easier packaging
- To increase solvent volatility
Correct Answer: To encapsulate drugs for controlled release or protect unstable drugs from the external phase
Q26. Which analytical parameter indicates surface charge of emulsion droplets and helps predict stability against aggregation?
- pH value
- Zeta potential
- Viscosity at 25°C
- Color index
Correct Answer: Zeta potential
Q27. Which oil property selection affects solubilization of lipophilic drugs in emulsions?
- Oil density only
- Oil polarity and solubility parameter (e.g., medium chain triglycerides vs mineral oil)
- Oil color
- Oil conductivity
Correct Answer: Oil polarity and solubility parameter (e.g., medium chain triglycerides vs mineral oil)
Q28. Which additive is used to prevent oxidation of oils in emulsions?
- Chelating agents like EDTA only
- Antioxidants such as butylated hydroxytoluene (BHT) or tocopherols
- Surfactants with high HLB
- Simple salts like NaCl
Correct Answer: Antioxidants such as butylated hydroxytoluene (BHT) or tocopherols
Q29. During formulation development, which experimental approach helps determine the optimal emulsifier blend?
- Single-factor-at-a-time without measuring droplet size
- Design of experiments (DoE) varying emulsifier type, concentration, and HLB to optimize droplet size and stability
- Only sensory testing by smell and color
- Storing samples without any stability testing
Correct Answer: Design of experiments (DoE) varying emulsifier type, concentration, and HLB to optimize droplet size and stability
Q30. Which in vitro test gives information about physical stability under accelerated conditions?
- Room temperature color check only
- Centrifugation and accelerated thermal cycling (freeze–thaw) studies
- Measuring pH only once at start
- Smell test after one day
Correct Answer: Centrifugation and accelerated thermal cycling (freeze–thaw) studies
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.
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