Suspending and emulsifying agents are essential excipients in pharmaceutical formulations, used to stabilize suspensions and emulsions by modifying interfacial properties and bulk rheology. B.Pharm students should understand mechanisms such as surface tension reduction, adsorption at interfaces, steric and electrostatic stabilization, and viscosity modification. Common suspending agents include xanthan gum, methylcellulose, and bentonite; emulsifying agents include lecithin, Tween, Span, and sorbitan esters. Key concepts include HLB, flocculation vs deflocculation, creaming, coalescence, particle size, zeta potential, and stability testing (sedimentation volume, centrifugation). Knowledge of selection criteria, compatibility and concentration effects is vital for successful formulation design. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which primary mechanism is used by emulsifying agents to stabilize oil-in-water emulsions?
- Increasing oil viscosity
- Reducing interfacial tension
- Raising aqueous phase pH
- Adding electrolytes to the oil phase
Correct Answer: Reducing interfacial tension
Q2. Which of the following is a natural suspending agent commonly used in oral suspensions?
- Carbomer
- Xanthan gum
- Sodium lauryl sulfate
- Polysorbate 80
Correct Answer: Xanthan gum
Q3. The Hydrophilic-Lipophilic Balance (HLB) value is primarily used to:
- Predict preservative efficacy
- Classify surfactants for stability of emulsions
- Determine polymer molecular weight
- Measure zeta potential
Correct Answer: Classify surfactants for stability of emulsions
Q4. Which parameter directly measures the degree of flocculation in a suspension?
- Viscosity at shear rate 100 s−1
- Sedimentation volume (F)
- Melting point
- pH of the suspension
Correct Answer: Sedimentation volume (F)
Q5. Which emulsifier is most suitable for forming water-in-oil (W/O) emulsions?
- Polysorbate 80 (Tween 80) with HLB ~15
- Sorbitan monooleate (Span 80) with HLB ~4.3
- Lecithin with HLB ~8
- Sodium lauryl sulfate with HLB ~40
Correct Answer: Sorbitan monooleate (Span 80) with HLB ~4.3
Q6. Which of the following is a primary role of suspending agents in pharmaceutical suspensions?
- Act as preservatives
- Increase settling rate
- Improve physical stability by increasing continuous phase viscosity
- Reduce osmolarity
Correct Answer: Improve physical stability by increasing continuous phase viscosity
Q7. Which test assesses the resistance of an emulsion to coalescence and phase separation under centrifugal force?
- Brookfield viscosity test
- Centrifugation stability test
- pH titration
- Flame point test
Correct Answer: Centrifugation stability test
Q8. A deflocculated suspension is characterized by:
- Formation of loose particle networks and rapid settling with compact cake
- Formation of flocs and high sediment volume
- Complete solubilization of drug particles
- Increased emulsion droplet coalescence
Correct Answer: Formation of loose particle networks and rapid settling with compact cake
Q9. Which surfactant class provides electrostatic stabilization by imparting charge to particle surfaces?
- Nonionic surfactants
- Anionic surfactants
- Sorbitan esters
- Polysaccharide thickeners
Correct Answer: Anionic surfactants
Q10. Which property of a suspending agent most influences the rheology of a suspension?
- Crystal structure
- Viscometric behavior (pseudoplasticity)
- Color
- Evaporation rate
Correct Answer: Viscometric behavior (pseudoplasticity)
Q11. In the context of emulsions, creaming refers to:
- Irreversible coalescence of droplets
- Migration of dispersed droplets under gravity forming a concentrated layer
- Formation of micelles in aqueous phase
- Hydrolysis of emulsifier molecules
Correct Answer: Migration of dispersed droplets under gravity forming a concentrated layer
Q12. Which polymeric agent is commonly used as a suspending and thickening agent for oral liquids and forms gels at low concentrations?
- Carbomer (Carbopol)
- Sodium chloride
- Mannitol
- Ethyl acetate
Correct Answer: Carbomer (Carbopol)
Q13. Which statement about nonionic emulsifiers is true?
- They provide charge stabilization by ionization.
- They are highly sensitive to pH and electrolytes.
- They stabilize emulsions mainly through steric hindrance.
- They always have HLB values above 20.
Correct Answer: They stabilize emulsions mainly through steric hindrance.
Q14. Zeta potential is used to predict:
- Thermal stability of emulsifiers
- Electrostatic stability of colloidal dispersions
- Viscosity at zero shear
- HLB value of surfactants
Correct Answer: Electrostatic stability of colloidal dispersions
Q15. Which of the following materials acts as both a suspending agent and a flocculating agent depending on concentration and medium?
- Bentonite (clay)
- Sodium benzoate
- Magnesium stearate
- Propylene glycol
Correct Answer: Bentonite (clay)
Q16. Which method is commonly used to prepare coarse emulsions in a pharmaceutical lab?
- High-pressure homogenization only
- Mortar and pestle trituration
- Shaking or stirring with a simple homogenizer (mechanical agitation)
- Spray drying
Correct Answer: Shaking or stirring with a simple homogenizer (mechanical agitation)
Q17. Which agent is typically used as a wetting agent to improve dispersion of hydrophobic powders in suspensions?
- Polysaccharide gum
- Surfactant such as sodium lauryl sulfate
- Silicon dioxide as a glidant
- Calcium carbonate
Correct Answer: Surfactant such as sodium lauryl sulfate
Q18. Which factor does NOT directly affect emulsion stability?
- Interfacial film strength
- Droplet size distribution
- Ambient humidity when sealed
- Viscosity of the continuous phase
Correct Answer: Ambient humidity when sealed
Q19. Which test provides quantitative data on viscosity of suspensions used for quality control?
- pH meter reading
- Brookfield viscometer measurement
- UV spectrophotometry
- Refractive index
Correct Answer: Brookfield viscometer measurement
Q20. Which of the following emulsifiers is a phospholipid commonly used in parenteral and oral emulsions?
- Poloxamer 188
- Lecithin (phosphatidylcholine)
- Carbomer
- Sorbitan monostearate
Correct Answer: Lecithin (phosphatidylcholine)
Q21. An increase in electrolyte concentration in a suspension of charged particles generally causes:
- Increased double-layer thickness and stronger repulsion
- Compression of the electric double layer and promoted flocculation
- Complete solubilization of particles
- Rise in melting point of the medium
Correct Answer: Compression of the electric double layer and promoted flocculation
Q22. Which emulsification parameter is most important to achieve small droplet size and long-term stability?
- Low shear mixing
- Appropriate choice of surfactant and adequate mixing energy
- High concentration of dissolved salts
- Absence of preservatives
Correct Answer: Appropriate choice of surfactant and adequate mixing energy
Q23. Which excipient acts primarily by steric stabilization when used as an emulsifier?
- High molecular weight polyethylene glycol (PEG)
- Anionic small molecule surfactant
- Strong electrolyte
- Low molecular weight alcohol
Correct Answer: High molecular weight polyethylene glycol (PEG)
Q24. The term ‘sedimentation volume’ in suspensions is defined as:
- Weight of sediment per mL of suspension
- Ratio of final sediment volume to original total volume
- Viscosity divided by density
- Concentration of suspending agent
Correct Answer: Ratio of final sediment volume to original total volume
Q25. Which preservative compatibility issue is important when formulating emulsions and suspensions?
- Preservatives always enhance emulsion stability
- Preservative may partition into the oil phase reducing antimicrobial efficacy in aqueous phase
- Preservatives increase HLB of surfactant
- Preservatives increase droplet size by evaporation
Correct Answer: Preservative may partition into the oil phase reducing antimicrobial efficacy in aqueous phase
Q26. Which measurement helps estimate the surface charge on colloidal particles in suspensions?
- Zeta potential measurement
- Infrared spectroscopy
- Thermogravimetric analysis
- Optical rotation
Correct Answer: Zeta potential measurement
Q27. Which class of agents is commonly added to emulsions to increase the viscosity of the continuous phase and reduce creaming?
- Viscosity enhancers like hydroxyethyl cellulose
- Antioxidants like BHT
- Solvents like ethanol
- Chelating agents like EDTA
Correct Answer: Viscosity enhancers like hydroxyethyl cellulose
Q28. For an oil-in-water emulsion, which HLB range is most suitable for the primary emulsifier?
- 1–4
- 4–6
- 8–18 (higher HLB)
- 20–30
Correct Answer: 8–18 (higher HLB)
Q29. Which phenomenon describes irreversible merging of emulsion droplets into larger drops?
- Flocculation
- Creaming
- Coalescence
- Osmosis
Correct Answer: Coalescence
Q30. When selecting a suspending agent for a parenteral suspension, which criterion is MOST critical?
- Color of the agent
- Pharmaceutical grade sterility and biocompatibility
- High odor intensity
- High hydrophobicity
Correct Answer: Pharmaceutical grade sterility and biocompatibility
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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