Definition and classification of emulsions MCQs With Answer

Definition and classification of emulsions MCQs With Answer
Understanding emulsions is essential for B. Pharm students: an emulsion is a heterogeneous system of two immiscible liquids where one liquid is dispersed as droplets within another. This introduction reviews definitions, pharmaceutical relevance, classification (oil-in-water, water-in-oil, multiple, micro- and nano-emulsions), emulsifying agents (surfactants, polymers, Pickering particles), stability mechanisms (interfacial tension, HLB, zeta potential, creaming, coalescence, Ostwald ripening) and preparation/evaluation methods. Emphasis is placed on formulation choices, evaluation techniques and therapeutic applications such as topical creams and parenteral lipid emulsions. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the most accurate definition of an emulsion in pharmaceutical sciences?

• A single-phase homogeneous solution of two miscible liquids
• A suspension of solid particles in a liquid continuous phase
• A heterogeneous system of two immiscible liquids with one dispersed as droplets in the other
• A gas dispersed in a liquid forming bubbles

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

Q2. Which pair correctly represents the primary classification of simple emulsions?

• Macroemulsion and microemulsion
• Oil-in-water (O/W) and water-in-oil (W/O)
• Liquid crystals and micelles
• Pickering and polymeric emulsions

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

Q3. Which statement correctly describes an oil-in-water (O/W) emulsion used in pharmaceuticals?

• Oil is the continuous phase and water is dispersed
• Water is the continuous phase and oil droplets are dispersed; commonly used for lotions and oral emulsions
• It is thermodynamically stable and forms spontaneously without surfactants
• It cannot be used for topical drug delivery

Correct Answer: Water is the continuous phase and oil droplets are dispersed; commonly used for lotions and oral emulsions

Q4. The HLB (hydrophilic–lipophilic balance) value of an emulsifier primarily indicates what?

• The molecular weight of the emulsifier
• The relative balance of hydrophilic and lipophilic portions that predicts suitability for O/W or W/O emulsions
• The electrical charge of the emulsifier
• The viscosity the emulsifier will impart to the emulsion

Correct Answer: The relative balance of hydrophilic and lipophilic portions that predicts suitability for O/W or W/O emulsions

Q5. Which of the following are common classes of emulsifying agents used in pharmaceutical formulations?

• Antioxidants, buffers and preservatives
• Surfactants, hydrophilic polymers and finely divided solid particles (Pickering stabilizers)
• Only proteins and polysaccharides
• Organic solvents and salts

Correct Answer: Surfactants, hydrophilic polymers and finely divided solid particles (Pickering stabilizers)

Q6. How do surfactant emulsifiers primarily stabilize emulsions?

• By increasing interfacial tension between oil and water
• By adsorbing at the oil–water interface, reducing interfacial tension and forming a protective film
• By dissolving the dispersed phase completely
• By chemically reacting with the drug molecule

Correct Answer: By adsorbing at the oil–water interface, reducing interfacial tension and forming a protective film

Q7. Which phenomenon is reversible and typically involves movement of dispersed droplets upward or downward without droplet coalescence?

• Coalescence
• Ostwald ripening
• Creaming
• Phase inversion

Correct Answer: Creaming

Q8. What is phase inversion in emulsions and how can it occur?

• Transformation of an emulsion into a solution by heating
• Conversion of O/W to W/O or vice versa due to changes in surfactant affinity (transitional) or high internal phase volume (catastrophic)
• Formation of micelles inside droplets
• Complete solidification of the continuous phase

Correct Answer: Conversion of O/W to W/O or vice versa due to changes in surfactant affinity (transitional) or high internal phase volume (catastrophic)

Q9. Which statement correctly characterizes microemulsions?

• They are kinetically stable and opaque with droplet size >1 µm
• They are thermodynamically stable, transparent or translucent, with droplet sizes typically in the 10–100 nm range
• They never require cosurfactants
• They are identical to macroemulsions in stability and appearance

Correct Answer: They are thermodynamically stable, transparent or translucent, with droplet sizes typically in the 10–100 nm range

Q10. Pickering emulsions are stabilized primarily by which mechanism?

• High concentration of low molecular weight surfactants
• Adsorption of solid particles at the oil–water interface creating a steric barrier to coalescence
• Electrostatic repulsion from ionic polymers only
• Formation of micellar structures in the continuous phase

Correct Answer: Adsorption of solid particles at the oil–water interface creating a steric barrier to coalescence

Q11. Ostwald ripening in emulsions refers to which process?

• Droplet aggregation without change in size
• Diffusive transfer of dispersed phase molecules from smaller to larger droplets, causing growth of larger droplets
• Immediate coalescence of all droplets after preparation
• Formation of a crystalline dispersed phase

Correct Answer: Diffusive transfer of dispersed phase molecules from smaller to larger droplets, causing growth of larger droplets

Q12. How does increasing internal phase volume fraction generally affect emulsion viscosity?

• Viscosity decreases as internal phase increases
• Viscosity remains unchanged regardless of internal phase
• Viscosity increases, often sharply, with higher internal phase fraction
• Viscosity becomes zero at high internal phase fractions

Correct Answer: Viscosity increases, often sharply, with higher internal phase fraction

Q13. Which natural phospholipid is widely used as an emulsifier in pharmaceutical formulations?

• Polysorbate 80
• Lecithin (phosphatidylcholine)
• Sodium lauryl sulfate
• Glyceryl monostearate

Correct Answer: Lecithin (phosphatidylcholine)

Q14. What defines a multiple (double) emulsion used in controlled release formulations?

• A single-phase micellar system
• An emulsion where droplets contain smaller droplets of the continuous phase, e.g., W/O/W or O/W/O
• An emulsion that has inverted to a solution
• An emulsion stabilized only by electrolytes

Correct Answer: An emulsion where droplets contain smaller droplets of the continuous phase, e.g., W/O/W or O/W/O

Q15. Which analytical technique is commonly used to determine mean droplet size and size distribution in emulsions?

• Gas chromatography
• Dynamic light scattering (DLS)
• UV–Vis spectrophotometry of the continuous phase
• Titration with a strong acid

Correct Answer: Dynamic light scattering (DLS)

Q16. What is the typical effect of adding a small amount of electrolyte to an ionic emulsifier system?

• Always increases emulsion stability by strengthening the surfactant film
• Can compress the electrical double layer around droplets, reduce zeta potential and promote flocculation
• Has no effect on electrostatic stabilization
• Instantly converts O/W to W/O emulsions

Correct Answer: Can compress the electrical double layer around droplets, reduce zeta potential and promote flocculation

Q17. Zeta potential measurement in emulsions is used to predict what property?

• The molecular weight of the emulsifier
• The degree of electrostatic repulsion between droplets and hence tendency to flocculate
• The exact droplet diameter in nanometers
• The pH of the internal phase only

Correct Answer: The degree of electrostatic repulsion between droplets and hence tendency to flocculate

Q18. Which of the following is commonly used as a preservative in aqueous phases of pharmaceutical emulsions?

• Parabens (e.g., methylparaben)
• Hydrogen peroxide
• Sodium chloride at 10% w/v
• Liquid paraffin alone

Correct Answer: Parabens (e.g., methylparaben)

Q19. Which is an example of a high-energy method commonly used to prepare fine emulsions and nanoemulsions?

• Gentle magnetic stirring
• High-pressure homogenization or microfluidization
• Simple mixing with a glass rod
• Room-temperature sonication without a probe

Correct Answer: High-pressure homogenization or microfluidization

Q20. Typically, which HLB range is more suitable for emulsifiers that form oil-in-water (O/W) emulsions?

• 0–3
• 3–6
• 8–18 (higher HLB values)
• 20–30 only

Correct Answer: 8–18 (higher HLB values)

Q21. What is the primary effect of adding a nonionic surfactant with a high HLB to an oil–water system?

• Promotes formation of water-in-oil (W/O) emulsions
• Reduces interfacial tension and tends to promote oil-in-water (O/W) emulsions
• Increases interfacial tension substantially
• Always causes phase separation

Correct Answer: Reduces interfacial tension and tends to promote oil-in-water (O/W) emulsions

Q22. Which instability mechanism leads to growth of larger droplets at the expense of smaller ones due to solubility differences?

• Creaming
• Flocculation
• Ostwald ripening
• Coalescence due to mechanical shear

Correct Answer: Ostwald ripening

Q23. Which formulation strategy helps reduce creaming in oil-in-water emulsions?

• Increasing droplet size and decreasing continuous phase viscosity
• Decreasing droplet size and/or increasing continuous phase viscosity
• Removing all emulsifier from the system
• Heating the emulsion to boiling point

Correct Answer: Decreasing droplet size and/or increasing continuous phase viscosity

Q24. Which type of emulsion is typically thermodynamically unstable but kinetically stable for a reasonable shelf-life?

• Microemulsion
• Macroemulsion (conventional emulsion)
• True solution
• Liquid crystal phase

Correct Answer: Macroemulsion (conventional emulsion)

Q25. For measuring very low interfacial tensions between oil and water phases in microemulsion research, which instrument is most appropriate?

• pH meter
• Spinning drop tensiometer
• Mass spectrometer
• Optical polarimeter

Correct Answer: Spinning drop tensiometer

Q26. At approximately what internal phase volume fraction does close packing of spherical droplets lead to drastic changes in emulsion rheology and often gel-like behavior?

• Below 10%
• Around 30%
• Approximately 74% (close-packed spheres)
• Exactly 100%

Correct Answer: Approximately 74% (close-packed spheres)

Q27. The cloud point of a nonionic surfactant is important because:

• It indicates the temperature at which the surfactant becomes ionic
• Above the cloud point the surfactant loses solubility in water and may cause phase separation or inversion
• It measures the pH stability of the emulsion
• It is unrelated to emulsion stability

Correct Answer: Above the cloud point the surfactant loses solubility in water and may cause phase separation or inversion

Q28. Which of the following is a common disadvantage of microemulsions in pharmaceutical formulations?

• They are always opaque and unstable
• They typically require relatively high concentrations of surfactant/cosurfactant which may lead to irritation
• They have very poor solubilization capacity for lipophilic drugs
• They cannot be sterilized

Correct Answer: They typically require relatively high concentrations of surfactant/cosurfactant which may lead to irritation

Q29. Which pharmaceutical application is an example of a parenteral emulsion?

• Topical cream for dry skin
• Oral emulsion for dyspepsia
• Intravenous lipid emulsion for parenteral nutrition
• Transdermal patch

Correct Answer: Intravenous lipid emulsion for parenteral nutrition

Q30. Which accelerated test is commonly used to assess physical stability and tendency for phase separation in emulsions?

• Centrifugation test to accelerate creaming and coalescence
• Direct tasting by a panel
• Chromatography to measure surfactant purity only
• Freezing without thaw cycles

Correct Answer: Centrifugation test to accelerate creaming and coalescence

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